files.eric.ed.gov · document resume. ed 431 290 ef 005 384. author loe, david; watson, newton;...

DOCUMENT RESUME

ED 431 290 EF 005 384

AUTHOR Loe, David; Watson, Newton; Rowlands, Edward; Mansfield,Kevin; Venning, Bob; Baker, John

TITLE Lighting Design for Schools. Building Bulletin 90.

INSTITUTION Department for Education and Employment, London (England).Architects and Building Branch.

ISBN ISBN-0-11-271041-7PUB DATE 1999-00-00NOTE 88p.; Colored photographs may not reproduce clearly.

AVAILABLE FROM HMSO Publications Centre, P.O. Box 276, London, SW8 5DTEngland; Tel: 0171-873-9090; Fax: 0171-873-8200 (22.95British pounds).

PUB TYPE Guides - Non-Classroom (055)EDRS PRICE MF01/PC04 Plus Postage.DESCRIPTORS Educational Environment; *Educational Facilities Design;

*Educational Facilities Improvement; Elementary SecondaryEducation; Energy Conservation; Foreign Countries; InteriorDesign; *Light; *Lighting Design; *Luminescence

IDENTIFIERS England

ABSTRACTThe aim of good lighting is to not only provide proper

illumination for building users to perform their allotted tasks, but also topleasantly enhance the indoor environment. This document guides architectsand engineers through the process of lighting design in the context of therecommended constructional standards for schools and the various types ofspaces and activities found in schools. It identifies the determining factors

of good lighting design as architectural integration, task and activitylighting, visual amenity, cost, maintenance, and energy efficiency. Further,it describes the calculation methods and design tools that can be used at theearly stages of a project and shows, using theory and examples, how toachieve a synthesis between daylight and electric light. Appendices presentschool premises regulations and Department for Education and EmploymentConstructional Standards for new school buildings, information on lightingand health, and details concerning various lamps, controlling gear, luminaryperformance ranges, lighting controls, disposal of used lamps, and examplesof lighting design strategies. A glossary concludes the book. (Contains 35references.) (GR)

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U.S. DEPARTMENT OF EDUCATIONOffice of Educational Research and ImprovementZUCATIONAL RESOURCES INFORMATIO

CENTER (ERIC)This document has been reproduced asreceived from the person or organizationoriginating it.

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BUILDING BULLETIN 90

Lighting Designfor Schools

Architects and Building Branch

London: The Stationery Office

AcknowledgementsDfEE would like to thank the following authors:

David Loe, Professor Newton Watson, Edward Rowlands and Kevin Mansfield of theBartlett School of Architecture, Building, Environmental Design & Planning,University College London, who started the research and wrote the original text;Bob yenning of Ove Arup & Partners, Research & Development for updating thetext;John Baker for the section on lighting for pupils with visual impairment.

DfEE would also like to thank :

Robin AldworthJohn LambertBob BellPaul RufflesProfessor Arnold Wilkins

DfEE Project TeamMukund PatelChris BissellRichard DanielsLucy WatsonKeith Gofton

Photographer:

Macintosh File:

Cover photograph:

formerly of Thorn Lighting Ltd.Gloucestershire County Councilformerly of Siemens Lighting Ltd.Lighting Design and Technology, BathDepartment of Psychology, Visual Perception Unit,University of Essex

Head of Architects and Building BranchPrincipal ArchitectSenior EngineerPrincipal ArchitectSenior Engineer, formerly of Architects &Building Branch

Philip Locker, Photo Graphic Design, Bolton

Malcolm Ward, Malcolm Studio, Croydon

Victoria Infants School, Sandwell MetropolitanBorough Council [Photo: P. Locker]

Published with the permission of the DiEE on behalf of the Controller of HerMajesty's Stationery Office.

@ Crown Copyright 1999

All rights reserved.

Copyright in the typographical arrangement and design is vested in the Crown.Applications for reproduction should be made in writing to the Copyright Unit,Her Majesty's Stationery Office, St Clements House, 2-16 Colegate, NorwichNR3 1BQ

First published 1999

ISBN 0 11 271041 7

4

Contents

1. Introduction 1

2. Components of lighting design 3

2.1 Task/activity lighting 3

2.2 Lighting for visual amenity 5

2.3 Lighting and architectural integration 5

2.4 Lighting and energy efficiency 6

2.5 Lighting maintenance 7

2.6 Lighting costs 7

3. Lighting options 8

3.1 Natural lighting 8

3.2 Electric lighting 12

3.3 Combined or integrated daylighting and electric lighting 14

4. Lighting design guidance 15

4.1 Day lighting 15

4.1.1 Daylight quantity 17

4.1.2 Daylight quality 19

4.1.3 Glare 194.1.4 Sunlight control 21

4.1.5 Exterior visual contact 224.2 Electric Lighting 23

4.2.1 Glare 244.2.2 Flicker and high frequency operation 244.2.3 Veiling reflections 244.2.4 Distribution of light 254.2.5 Choice of lamp and luminaire 27

4.3 Integrated daylight and electric light 284.4 Aids to lighting design 29

5. Lighting for particular applications 31

5.1 Circulation areas 31

5.2 Areas with display screen equipment 345.3 Science work and laboratories 365.4 Design and technology rooms and workshops 375.5 Libraries 375.6 Art rooms 385.7 Sports halls and gymnasia 385.8 General purpose halls (examination, assembly, performances and PE)

and drama & dance studios 405.9 The lighting of chalkboards 415.10 Lighting and visual aids 425.11 Lighting for pupils with visual and hearing impairments 425.12 Local task lighting 455.13 Exterior lighting 455.14 Emergency lighithg 47

Contents

6. Check-list for lighting design 48

6.1 Task/activity lighting 486.2 Lighting for visual amenity 486.3 Lighting and architectural integration 486.4 Lighting and energy efficiency 486.5 Lighting maintenance 496.6 Lighting costs 496.7 Exterior and emergency lighting 49

Appendices: 50

1. School Premises Regulations and DfEE Constructionalstandards for new school buildings 50

2. Lighting and health 51

3. Lamps 524. Control gear 555. Luminaires 566. Lighting controls 607. Disposal of used lamps 628. Examples of lighting design strategies 64

8.1 Site analysis 648.2 A typical classroom 678.3 An atrium 71

Glossary 77

Bibliography 81

6

Section 1: Introduction

The best school environments give animpression of liveliness, with attractivespaces and a general feeling ofpleasantness which it is difficult to define.There can be no doubt that in these casesthe surroundings contribute to thehappiness and well-being of teachers andpupils, and that lighting plays a significantif not the leading role. Lighting (bothnatural and electric) will be recognised asan essential contribution if it stems fromand encourages the fulfilment of schoolactivities.

The aim of good lighting rather thanbeing a purely formal exercise to provideenough illumination to enable buildingusers to go about their tasks safely andcomfortably, though this must always be aprime aim, is to create a pleasantenvironment which enhances the buildingform and is in sympathy with thearchitectural intention.

Natural lighting during daylight hoursshould always be the major source,supplemented when it fades by electriclight which will take over during hours of

the internal view is sufficiently long thereis no necessity for an extensive externalview, provided that they are not used forexcessively long periods of teaching.

Window design, particularly in ournorthern climate, forms a crucial part ofthe architect's vocabulary, requiring adelicate balance between formal decisions,on proportion for example, and functionalconsiderations. Surprisingly, though muchof the internal and external character ofbuildings derives from fenestration design,one often finds otherwise attractiveenvironments being marred by a

darkness. The reasons for this need fornatural light stem both from theimportant link with the outside whichwindows provide and the essentialcharacter of daylight and its changingvalue throughout the teaching day whichelectric light cannot replicate. Thoughdesirable, it is not always possible tocombine arrangements for admittingdaylight with views out, although somewindow area for views out is essential;teaching and spatial needs sometimes callfor glazed internal spaces, for examplewhere natural light is admitted throughclerestories and/or rooflights. In thesecases, often called atria, it appears that if

disruption of this balance. Underglazingcan make interior spaces dismal andgloomy, whilst overglazing can createexcessive solar gain in summer andexcessive heat loss in winter withattendant discomfort. Lack of attention

71

Section 1: Introduction

to detailed window design can result inpoor visual conditions, inefficientventilation and an unattractive space.

The design of electric lighting is part ofthe whole architectural scheme, butsufficient care is not always taken toprovide the necessary visual variety andstimulation, though schemes are usuallyadequate quantitively.

One of the attributes of electriclighting inherently absent from naturallight is its flexibility to demand, a featurewhich can be harnessed in certain cases toenhance the brightness of vertical planesin positions adjacent to and away fromwindow walls, a fact which can beexploited and used to good effect as asupplement to natural side lighting.

It is necessary to understand the meansby which daylight is admitted to schoolsand to have an overview of thecharacteristics of electric lighting systems.The two are interdependent and in thebest designs this fact is understood andacted upon.

The aim of this bulletin is to giveadvice and examples of how a propersynthesis can be and is achieved. Thebulletin has a 'layered approach'. It takesthe reader from the basic range oflighting considerations which will help in

2

determining particular aims, to thestructure of lighting design. It then goeson to consider various lighting optionsavailable and the implications resultingfrom them. The section on lightingdesign aims to provide positive guidancewhere appropriate, but not to stiflecreativity.

Towards the end of the publication acheck-list has been included. This is tohelp the designer to ensure that no aspecthas been overlooked. It will also behelpful to school staff to derive the mostbenefit from the lighting provided interms of the use of spaces and themaintenance of these systems.

The publication addresses the lightingof both primary and secondary schoolsbut it does not differentiate betweenthem.

All schools have a range of spaces,many of which are used for a number ofdifferent activities, either at the same timeor at different times. It is importanttherefore for the designer to identify theparticular activities that will, or are likelyto take place in each of the spaces, inorder to achieve appropriate lighting. Alarge part of the document concentrateson the 'general teaching spaces', withadditional information for areas withspecific requirements.

No differentiation has been madebetween lighting design for new andrefurbished buildings, although theopportunities available to the designerwill not be exactly similar, as thefundamental lighting requirements arethe same in both cases.

It is hoped that this bulletin willprovide designers with advice andguidance to help them develop successfulschools in the future.

5

Section 2: Components of Lighting Design

The lighting design for a school needs to provide a litenvironment which is appropriate for the particularinterior and indeed exterior, achieving lighting whichenables students and staff to carry out their particularactivities easily and comfortably in attractive andstimulating surroundings.

In considering the design it is necessaryto take into account a range of differentand perhaps conflicting requirements andto do this bearing in mind the possibleconstraints. It is also necessary to considerthe overall architectural concept and inturn the determinants which will enable itto be achieved. Whilst each element isimportant, and must be considered, theemphasis placed on each facet may notbe equal.

Figure 1 illustrates the main areas ofconsideration for lighting design, togetherwith the determining features and anindication of how they relate to eachother. The following parts of this sectiondescribe the elements of the framework tohelp the designer to develop a strategy.

Figure 1: Framework showingmain components of lightingdesign & determining factors.

LIGHTING & ARCHITECTURALINTEGRATION

Natural lighting designAppearance of lighting equipment

Electrical lighting installationLighting controls

Integration of natural & electric lighting

LIGHTING COSTSCapital costs of installationRunning costs of installation

LIGHTING FOR VISUAL AMENITYLight pattern

Overall lightnessColour appearanceDiscomfort glare

Disability glareFlicker

External & internal view

2.1 Task/Activity LightingFunctional lighting or task lighting is thatwhich enables users to carry out theirvarious tasks and activities easily andwithout visual discomfort and it isimportant that the designer assesses theserequirements carefully.

For general teaching spaces a level oflight is required which makes it easy tocarry out quite small and difficult tasks.Reading and writing, typical schoolactivities, require a minimum kw:: ofilluminance with a relatively highilluminance uniformity over the task area.Higher levels should be used for moredetailed work and for parficularlydemanding visual tasks, such as using amachine in the workshop or studying finedetail in the art room. The higher levelscan be provided by using an adjustabletask light to supplement the generalilluminance in the particular area required(Fig. 2) or by providing localised lightingto complement the general or ambientlighting. Localised lighting is permanentlyinstalled lighting equipment which

TASK/ACTIVITY LIGHTINGTask illuminance

Task illuminance uniformityColour renderingDiscomfort glareDisability glare

Flicker

LIGHTING MAINTENANCELamp replacement

Luminaire typeCleaning & redecoration programme

Lamp disposal

LIGHTING & ENERGY EFFICIENCYNatural lighting design - windows,etc

Lamp typeLuminaire type

Lighting controlsIntegration of natural & electric lighting

RFST COPY AVNLABLE


Figure 2: Use ofsupplementary local tasklighting. [Photo: P. Locker]

provides the increased illuminance whereand when it is required (Fig 3). If,however, it is impossible to define thearea where a higher illuminance may berequired, then it will be necessary toprovide the increased illuminance over thewhole area.

Another aspect of task lighting whichneeds to be considered is helping todefine the three-dimensional qualities ofthe task, ie, its shape and surface texture.This will demand a directional quality inthe lighting, ie, a flow of light, and can beprovided for example by natural lightfrom side windows or electric lightingused to enhance the brightness of avertical surface.

Colour plays an important role inlearning and light sources should have agood colour rendering performance: this

Figure 3: Complementarylocalised lighting using lines ofsuspended fluorescentluminaires and displayspotlights either side of acentral rooflight fitted withlouvre blinds (see also Fig. 22).[Photo: P. Locker]

4

will enable accurate colour judgements tobe made. Because this requirement isnecessary for a number of schoolactivities, eg, art, science and craftsubjects, it is recommended that a goodcolour rendering light source is used in allteaching spaces.

Colour and contrast are particularlyimportant to the hearing impaired andthe visually impaired (see 5.11). Forexample, downlights in reception orteaching areas produce harsh shadowswhich obstruct lip reading, and use ofelectrical socket outlets with backplates ofcontrasting colour located at a standardheight is helpful to the visually impaired.

Visual comfort is also very important,and to avoid the possibility of eye strainand headaches it is necessary to limit thebrightness range within the normal fieldof view. Discomfort can be caused forexample by electric lighting equipment,views of the sky, or of bright lights beingreflected in the task such as a computerscreen or glossy reading material. Directsunlight can also be a problem in thisrespect depending on the orientation ofthe window and its design, and it isimportant that these potentially glaringsources are avoided. Another aspect ofvisual comfort is concerned with flickerfrom discharge lamps which, in somecases, has been shown in recent researchto cause discomfort. It is possible now touse luminaires that operate at very high

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frequencies and largely overcome thisproblem.

It is essential to analyse thetask/activity requirement beforedesigning the lighting.

2.2 Lighting for Visual AmenityProviding suitable lighting for the tasksand activities of a school is of courseimportant, but it is equally important toprovide lighting that enhances theappearance of the space lighting forvisual amenity. To do this, it is necessaryto light the space so that it appears'bright' and 'interesting'. Light surfaces,particularly the walls and perhaps theceiling too, contribute to this impression.It is also desirable to achieve a degree ofnon-uniformity in the light pattern, asspaces which have areas of light and shadeare generally liked, but it is important forthis variation in brightness not to be toogreat, otherwise poor visibility or evenvisual discomfort may result.

The colour appearance of the electriclight will also need to be consideredbecause different lamp types producedifferent degrees of 'warmth' or 'coolness'.

Throughout a school, not only willthere be a need for bright and airy spaces,modulated with light and shade, but therewill also be a need for areas that are moreprivate and secluded. An example of thisis a story-telling area in a primary school.


In this case the designer may like toconsider providing an internal space litonly by electric lighting where the patternof light is arranged to accent the storyteller. A similar effect could be producedwith a small rooflight. A corridor or anentrance area are other places where thelight pattern should vary to provide smalldisplay areas for objects or pictures. Thedisplay areas would need to be the brightso that they attract attention.

Whilst direct sunlight on the task areacan be a problem, an additional considera-tion in visual amenity is the enhancementof the environment by the appearance ofsunlit areas; these could be in circulationspaces or in the exterior view.

Lighting for visual amenity is asimportant as task lighting anddepends on the balance andcomposition of light and shade.

2.3 Lighting and ArchitecturalIntegrationThe lighting of a building, both naturaland electric, should enhance thearchitecture, and to achieve this, theelectric lighting installation should be anintegral part of the whole and not anappendage. Equipment should be selectedto harmonise with the architecturalconcept and this applies equally to electriclighting equipment and the detaileddesign of windows. In addition, the

Figure 4: Tipton Infants'school, Sandwell. Combinationof side window, clerestory lightand linear electric lightingsystem. [Photo: P. Locker]

.E 5


Figure 5: Pattern of lightenhancing the building form.Farnborough Grange JuniorSchool. [Photo: Martin Charles]

6

pattern of light must enhance the buildingform and be in sympathy with it, care beingtaken to ensure that projected patterns oflight respond to this need. (Fig 5)It has already been stressed that mostparts of a school should appear bright andinteresting, and that whilst lighting canmake a major contribution to this, thereflectance and colour of the mainsurfaces will also have a major effect. It issuggested that the main surfaces of theinterior are light in colour if the space isto appear light. If however there is arequirement for a more secluded spacethen darker finishes may be used. The useof strong surface colours should not bediscounted but they need to be usedsparingly.

One of the most important reflectingsurfaces in a building is the floor and it isimportant to have this light in colour.Light carpets are likely to suffer earlydeterioration in general teaching spacesbut there are other materials which haveboth a light finish and can be easilycleaned.

For the lighting to function well from

the users' point of view, and be energyefficient, it will need to have thecontrolling switches designed andpositioned to fit in with the use and shapeof the space. By considering this aspectearly in the design process the controllingcircuits can be organised to allow theelectric lighting to complement thenatural lighting in a positive and energyeffective way. They can also be organisedto respond to the uses of the space, eg,providing accent lighting on separatecircuits to the general lighting. All thesematters are dealt with later.

Both electric and natural lighting mustbe an integral part of the architecture.

2.4 Lighting and Energy EfficiencyAn effective and efficient use of energy isan important aspect of any lightingproposal and school buildings are noexception. This is in order to minimisethe use of primary energy and hencereduce carbon dioxide emissions and also,of course, to reduce the running cost ofeach lighting installation.

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When planning energy efficiency inlighting it is necessary to considerdaylighting and electric lighting bothindividually and in conjunction with oneanother. An extensive use of naturallighting can provide considerable energysavings but daylight is not 'free' and theother environmental aspects of largeglazed areas must be taken into account.Similarly, by the careful selection ofenergy efficient electric lightingequipment, installed in an energy effectiveway, together with controls whichencourage the use of electric lighting onlywhen it is required, an energy efficientlighting system can be achieved. It wouldbe futile to create such an energy efficientscheme if the result was compromised interms of performance and appearance. Inthese circumstances, users will oftenattempt to improve the lightingthemselves, and perhaps, in doing so,destroy the energy efficiency planned.

An effective use of energy in lighting isan essential part of lighting design.

2.5 Lighting MaintenanceDuring the life of a lighting installationthe amount of light it produces willdiminish. This reduction is caused mainlyby dirt building up on the lamps, theluminaires, or in the case of naturallighting, on the windows. There will alsobe a reduction caused by dirt build-up onthe internal surfaces of the rooms,diminishing their reflectance. Lamp lightotftput will also reduce with ageing.

These reductions in lighting levels willneed to be minimised if energy andmoney are not to be wasted, and to dothis it is important to pay attention at thedesign stage to the proper maintenance ofthe lighting installation and of thebuilding itself. This aspect should bediscussed in advance with the users of thebuilding to ensure that they are aware ofthe proposed maintenance strategyand its implications and obtain theirco-operation.

Poor maintenance is a cause of badlighting and is also a waste of energyand money.

Section 2: Cornponents of Lighting Design

2.6 Lighting CostsThe cost of lighting can be divided intotwo parts; the capital cost of theequipment including its installation andthe running costs which include bothmaintenance and the cost of energy. It isimportant that both aspects areconsidered when the lighting is beingdesigned. In terms of capital cost, theamount will be small compared to thetotal cost of the building and yet lightinghas a major effect on its appearance andoperation, and economies need to beconsidered carefully to ensure that theyare not false economies. Energy andmaintenance costs are a continuingburden on the operation of a school andneed to be taken into account at thedesign stage to ensure that they can bekept at an acceptable level.

For many schools, the two costelements may be borne by differentbodies which can result in a conflict ofinterests. It is important therefore thatthe lighting designer produces a schemewhich takes a balanced view of energy andcost efficiency, considering both capitaland running costs.

Consider both capital and runningcosts in concert and avoid falseeconomies.

Swimming pool luminaires overpool surround for ease ofmaintenance and safety(broken glass is a hazard).

7

Section 3: Lighting Options

Figure 6: Options andelements to be considered inlighting design.

Figure 7: Combination of sideand top light. BerrywoodPrimary School, Hedge End,Hampshire. [Photo: Joe Low]

RKTU ALIIONIUGG DESIGN

Room orientation

External obstruction

Sun-screening & re-direction

Windows in relation to view

Rooflights & clerestories

Atria & borrowed light

Rodrn .size and Shate

Furnishings

--Room surface colours& reflectances

IVTairitenance

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ELECTRLamm immaq

Lamps

Luminaires

Lighting controls

Lighting installation

The diagram above shows the mainlighting options natural lighting, electriclighting or a combination of the two,together with the elements which need tobe considered. These are examined inmore detail in the following sections.

8

3.1 Natural LightingUnless there are over-riding

educational reasons for not doing so incertain rooms, the school designershould assume that daylight will be theprime means of lighting when it isavailable. This is both because of theunique quality of natural light and thelink with the external environmentwhich windows of all types provide.However, in addition to providingdaylighting and a view out, windows canbe a source of annoyance and sometimesdiscomfort, for instance when there is aparticularly bright sky or when there issun penetration which disrupts theactivities within the space. Both skylightand sunlight need to be considered, andthe building should be planned to takeaccount of space organisation in relationto orientation. Windows can also havean effect on other environmental factors,particularly thermal comfort, fresh airsupply, energy efficiency and noiseintrusion. It can be seen therefore thatwindows are a complex part of buildingdesign and need careful consideration formaximum benefit and pleasure togetherwith minimum dissatisfaction.

The means for admitting daylight can-be broadly classified as follows (Fig 8):

Side windows have the advantage thatthey permit a view of the outside,provided that their heads and cills are atthe correct level and that there are no

4


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a. Side windowsb. Clerestory windowsc. Rooflightsd. Borrowed lights

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intrusive transoms to obstruct this view atsitting and standing eye level positions forchildren and adults (Fig 9). It is moreusual for trees, other buildings and risingground to cause an obstruction in thecase of side windows, though there is ofcourse an externally reflected componentof light from these obstructions.

The shape and position of windowsaffects the way in which daylight isdistributed, wide shallow windows givinga broad distribution and tall narrowwindows a deep but narrow distributionfor instance (Fig 10).

Clerestory windows admit light fromthe brighter part of the sky and this isunlikely to be obstructed: an importantfeature of clerestory windows or of anyhigh level window is that they can providedaylight deep into a space.

However, there is a higher probabilityof the contrast between inside and outsidecausing glare. They will probably not givea direct outside view but do provideinformation about weather conditionscloud formation etc. Clerestory windowsare usually found in single storeybuildings or in those with a complexsection (Fig 8).

Rooflights also admit light from thehighest and brightest part of the sky, andwill not generally be affected by externalobstruction; they need the same care indesign to take account of glare from

BEST COPY MORE

contrast as do clerestory windows, and togive the same information about theexternal environment. They have thetendency to provide a more even patternof light. It goes without saying thatsimple rooflights can only be employed insingle storey buildings or on the top floorof multi-storey buildings. Light-wells arehowever a possibility in multi-storeybuildings (Fig 12).

Borrowed lights. In certain cases, whererooms open off a corridor which is top litfor example, or are arranged around a toplit larger space or atrium, borrowed lightcan make a contribution to the light levelsin areas remote from window walls (Figs11 and 12). Although the supplement isoften quite small it can help to improvethe appearance of the space quiteconsiderably.

Figure 8: Window types.

Figure 9: Detailed windowdesign to avoid obstruction ofview.

_...._..

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a. care over cill heightb. care over transom positionc. care over window head height and external projection

9


Figure 10: Indicates therelationship betweenwindow/rooflight shape andposition, and light distribution.

10

Wide distribution

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Wide distribution away from window

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Concentration on horizontal plane

Deep distribution

w/w

Corner windows also light window walls(w/w)reducing contrast

Roof light highlights the adjacent wall

Atria. These are large internal spaces withrooflights or clerestory windows. Inschools, they are usually single or doubleheight spaces and have the advantage ofproviding attractive views for the spacesaround their perimeter, although theamount of light penetration to thesespaces may be small, particularly atground floor level. The atrium can beused for a variety of teaching purposes,but care will need to be taken overthermal comfort, ie, heat loss in winterand heat gain in summer. These problemscan be overcome with careful

consideration of sun penetration and suncontrol, together with the design of theroof, selection of glazing materials andthe design of natural ventilation using thestack effect. The view into the atrium andthe appearance of the atrium itself may beimproved by planting. However, careneeds to be taken to ensure that theenvironment is suitable for the plantsselected. Care will also need to be takento avoid visual discomfort throughoverglazing and some form of blinds maybe necessary. Some of theseconsiderations are discussed further in the

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illustrative example in Appendix 8.3.For all these window types, the sun's

angle at various times of day and yearshould be studied as sun penetration canpresent a problem. However, the benefitsprovided by the appearance of sunlitviews, particularly in non-task areas,should not be overlooked (Fig 12).

Wmdows provide a considerablebenefit to school buildings: considerskylight, sunlight, views out and otherrelated environmental matters

Figure 11: Diagram showingborrowed light from rooflight

helping to light rooms 'A'and 'B' by direct and reflectedlight.

Figure 12: Borrowed light torooms from central atrium.Bottom left: Fareham TertiaryCollege. [Photo: Joe Low]Right: Whitefield School,ground and first floors, withlight wells to ground floorcorridor. [Photo: P. Locker]

11

17


Table 1: Distribution of lightfrom luminaires (see diagramsin Appendix 5).

12

3.2 Electric LightingWhen daylight fades, on dull days andduring the hours of darkness, it isnecessary to turn to electric lighting.Here, as in daylighting, there are manyoptions. The areas that need to beconsidered are the light sources, theluminaires, the controls and theinstallation itself.

The most common light source foundin schools is the linear fluorescent typewhich can be used to provide a relativelyeven pattern of light. These lamps cangive good colour performance, ie, colourrendering and colour appearance, goodefficacy and good optical and electricalcontrol. The more recently introducedcompact fluorescent lamps (CFL) can beused either for general lighting or for taskand accent lighting, and the smallerversions are a good alternative totungsten filament lamps. These lamps alsoprovide good colour performance andgood efficacy but only a few can currentlybe dimmed.

The tungsten filament lamp togetherwith the linear halogen lamp have beenused extensively in the past, particularlyfor their low capital cost, compact size,good colour performance and ease ofcontrol. These lamps however do have apoor efficacy and a relatively short life andthe designer would be well advised toconsider compact fluorescent lamps as analternative. Reflector lamps whichinclude low voltage versions (12 volts

supplied from a small transformer) andhave an integral reflector are available forspecial display purposes. These reflectorlamps have a longer life than the tungstenfilament type but are much less efficientthan the CFL type.

The last group of lamps consideredhere is the high pressure discharge type.This includes high pressure sodium, highpressure mercury fluorescent and highpressure metal halide lamps. Within thisgroup the lamps vary in terms of colourrendering and colour appearance and thisneeds to be considered in making aselection for a particular situation. It isalso important to note that these lampshave a time delay before reaching theirfull light output after being switched onand in restriking after being switched off.

The selection of luminaires will dependon the level and pattern of light required.The level of light or illuminance, willdepend on the light output intensity ofthe luminaire and its distribution. Thedistribution can be first considered byreference to the simple categoriesshown in Table 1 below.

This is a relatively simple classificationof a luminaire's light output distributionbut it will help the designer to appreciatethe type of light pattern that will result. Itshould be noted that some luminaires donot have a symmetrical light outputdistribution, ie, wall washing luminairesand wall mounted indirect luminaires.

The equipment selected should be

Category Upward Light

Direct 0 10% / \Semi-direct 10 40%

General diffusing 40 60%

Direct-Indirect 40 60%

Semi-indirect 60 90%.

Indirect 90 100% at/

chosen to be in sympathy with thearchitecture. It is necessary to considerthe way that luminaires are installed, ie,surface mounted on the ceiling or walls,recessed into the ceiling, or integratedinto the building structure in some otherway (Fig 13).

A common method of lighting schoolsis to use a regular array of ceilingmounted or suspended luminaires. Thesewill provide a general wash of light whichmay be acceptable for lighting the taskbut will produce an even pattern of lightwhich can often appear bland. If these areindividually mounted or suspended, theywill tend to make the ceiling appearcluttered. This can be overcome by usingone of the continuous lighting systemswhich can combine direct, indirectand/or accent lighting (Fig 13).

Ceiling recessed luminaires are anotherpossibility and they produce a moreintegrated appearance, but because theyare recessed they provide no direct lighton to the ceiling, and this can make thespace appear underlit. However, if thistype of installation is used with a highreflectance floor, then it may be perfectlyacceptable.

Indirect or uplighting luminaires canbe used which will generally produce


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Figure 13: Top: BurnhamCopse Infants' School[Photo: R Brooks, HampshireCounty Counci0Left: Victoria Infants' School,Sandwell M.B.C.[Photo: P. Locker]

13


Left Queen Elizabeth School,Alford, Lincs.Right Victoria Infants' School,Sandwell M.B.C.(Photo: P. Locked

'light' ceilings and shadowless lighting.It has already been stressed that some

of the internal building surfaces shouldappear 'light', particularly walls andceilings. To achieve this it will sometimesbe necessary to light preferentially thesesurfaces by using wall-washing luminairesand uplighting. However this approachmust not be applied to all such surfaces orthe lighting will appear bland anduninteresting.

The most effective electric lightinginstallations are those comprising differentelements which combine in terms of taskand appearance, eg, general lighting, tasklighting and accent lighting.

Although electric lighting dependsprimarily on the equipment, it is necessaryto take into account the reflectance of themain surfaces of the space as well as thefurnishings, and also the possible lightobstruction caused by the furniture andother objects within the building.

The electric lighting installation mustprovide for visual ability and amenity,be an effective use of energy and be insympathy with the overall design ofthe building.

3.3 Combined or IntegratedDaylighting and Electric LightingIn school buildings most of the spaceswill be predominantly daylit, with electriclighting taking over on dull days and atnight. There will however be some spaceswhich have some daylight, but not alwayssufficient over the whole area. In thesecases, it will be necessary to employ asystem combining both daylight andelectric lighting which is used as andwhen required. It will be necessary toconsider the distribution of daylighttogether with the complementary electriclighting distribution to ensure theyenhance one another. However, it will notbe sufficient to provide a combinedlighting system that only gives a uniformhorizontal plane illuminance. It will alsobe necessary for the electric lightinginstallation to create the sensation ofbrighmess in the areas remote from thewindows. For this it will be necessary tohighlight surfaces, particularly the walls.

For combined lighting installationsconsider both the task and theappearance effects.

14 41'

fl

Section 4: Lighting Design Guidance

4.1 Day lightingAs mentioned earlier, it is generallyconsidered that schools should havenatural lighting whenever possible.Natural lighting, however, is very variableand for design purposes, direct sunlight isexcluded and an overcast sky with adefined luminance distribution is specified:in the UK, the CIE (CommissionInternationale de l'Eclairage) StandardOvercast Sky distribution is used.

The design measure used is theDaylight Factor which is the percentageof the horizontal diffuse illuminanceoutdoors from an unobstructed skyhemisphere which is received at a pointindoors: there are three components thecomponent received directly from the sky(Sky Component), the componentreceived by reflection from externalsurfaces (Externally ReflectedComponent) and the component receivedby reflection from internal surfaces(Internally Reflected Component) (Fig14). The Daylight Factor will vary withina space depending on a number ofparameters including the size anddisposition of the glazing, the dimensionsof the space, the reflectance of theinterior surfaces and the degree ofexternal obstruction.Interiors with an Average Daylight Factorof 5% or more are considered to be day-litrooms and will not normally requireelectric lighting.

Interiors where the Average DaylightFactor is below 2% will require frequentuse of electric lighting.

Interiors where the Average DaylightFactor is between 2% and 5% will requiresome electric lighting between Octoberand March. To take full advantage of theavailable daylight will require anautomatic daylight linked control system.

The Average Daylight Factor (DF) can beestimated from the following formula:

DF T W 0 %A (1 R2)

Where:

T = diffuse transmittance of glazing materialincluding effects of dirt (see note)

W = net glazed area of window (m2)

o = angle in degrees subtended, in thevertical plane normal to the window, bysky visible from the centre of the window(Fig 15)

A = total area of interior surfaces includingwindows (m2)

R = area-weighted average reflectance ofinterior surfaces, including windows(see Table 3)

Note: Typical transmittance values for clean,clear single and double glazing are 0.80 and0.65 respectively. For the value T, the glasstransmittance will need to be multiplied by afactor to take account of dirt on the glass:suitable correction factors are given in table 2.

Sky componentExternally reflected component

Internally reflected component

BEST COPY AVMLABLE 61'.

Figure 14: Daylight factorcomponents

15


Figure 15: Angle 43 whichdefines visible sky from centreof window/rooflight

Table 2: Correction factors totransmittance values for dirton glass.

Table 3: Approximatereflectance values for varioussurface finishes.

16

00'

00'

Correction factors for dirt on glass.Type of Vertical Sloping Horizontallocation glazing glazing glazing

clean 0.9 0.8 0.7indUstrial 0.7 0.6 0.5very dirty 0.6 0.5 0.4

Reflectance values will vary depending onthe surface finish: approximate values forsome paints and materials are given in thefollowing table.

Paint coloursWhitePale creamLight greyMid-greyDark greyDark brownBlack

Internal materialsWhite paperCarpetBrickworkQuarry tilesWindow glass

Reflectance0.850.80.70.450.150.10.05

0.8

0A5-0103-02OAOA

More paint colours and materials aregiven in Tables 5.8 and 5.9 of the CIBSECode for Interior Lighting. Informationfor other glasses and particular surfacefinishes should be obtained frommanufacturers.

The glazing area for a required AverageDaylight Factor can be obtained from are-arranged formula.

The above formula is applicable tovertical glazing and to some rooffights:rooffights which have an upstand or skirtrequire an additional term to take accountof inter-reflection and absorption (seeCIBSE Applications Manual: WindowDesign).

It is also useful to consider theuniformity of the daylight. TheUniformity Ratio is defined as theMinimum Daylight Factor/AverageDaylight Factor. A Uniformity Ratio inthe range 0.3 to 0.4 is recommended forside-lit rooms. Where spaces are top-lit,eg, atria, then higher uniformities shouldbe expected of the order of 0.7.The Minimum Daylight Factor value,required for the estimation of theUniformity Ratio, can be obtained bymeans of one of the commerciallyavailable computer programs or using oneof a number of tabular or diagramcalculation methods which are describedin Part B1 of CIBSE ApplicationsManual: Window Design. The position ofthe Minimum Daylight Factor can usuallybe estimated from a study of the roomplan relative to the window placing.The purpose of using the daylight


'no-sky' pointworking plane

Uniformity Ratio as part of the designcriteria is to ensure that a daylit roomdoes not have any areas which will appeardark. Another way of considering thisaspect of design is to take account of the`No-sky line'. This is the line, on the flooror horizontal working plane, beyondwhich no direct light from the sky willreach. The area beyond this line willusually receive very low levels of naturallight and this will usually requiresupplementary electric lighting (Fig 16).

4.1.1 Daylight QuantityBy the definition of Daylight Factor (DF),the illuminance provided by the daylightcan be determined from:

Interior ExteriorDE

Illuminance = Illuminance X XOrientation

100 Factor(lux) (lux)

100

80

60percentage of yearfor which a givendiffuse IlluminanceIs exceeded 40

20

0

The Window Orientation Factor isintroduced because even with overcastskies, there is a noticeable variation inluminance, with the southern sky havingthe greatest effect. Values of OrientationFactor are given in the following table(for a 09.00 17.00 day):

Orientation Orientationof Window FactorNorth 0.97East 1.15South 1.55West 1.21For intermediate orientation, linear interpolationcan be used.

In determining the illuminanceprovided by daylight, the variability of theexterior illuminance must be taken intoconsideration, and Figures 17 and 18provide data on the availability of daylightfor a typical year for both London andEdinburgh.

9.00 - 16.009.00 - 17.009.00 - 19.00

0

BEST COPY AVAILABLE

20 ao 60 80

diffuse illuminance (lux x 1000)

1 9

Ct.:1 ce0 6.

Figure 16: No-sky line: locusof points beyond which thereis no direct light from the sky.

Table 4: Window orientationfactors for calculation ofinterior illuminance.

Figure 17: Daylight availabilityfor three different lengths ofday in London.

17


Figure 18: Daylight availabilityfor three different lengths ofday in Edinburgh.

Note: Figures 17 and 18 from

BS8206: Part 2: 1992 arereproduced with the permission of

BSI. Copies of complete standards

can be obtained by post from BSI

Publications, Linford Wood, Milton

Keynes, MK14 6LE.

Figure 19: Queen's InclosureMiddle School, Cowplain,showing use of rooflight incentre of building. [Photo: RBrooks, Hampshire CountyCouncil]

18

100

80

60

percentage of yearfor which a givendiffuse illuminance

40is exceeded

20

9.00 16.009.00 17.009.00 - 19.00

20 40 60 80

diffuse illuminance (lux x 1000)

In order to achieve the daylightrecommendations in rooms lit from oneside, it can be useful in single-storeybuildings and the top floor of multi-storey buildings to consider the additionaluse of rooflights or clerestory lightsremote from the windows. This canproduce an improved distribution of lightin the space (Fig 19). The estimation ofthe combined effect of the individualparts for the average daylight factor canbe made using the method describedabove. (For further details see CIBSEApplications Manual: Window Design).

However, when the daylightrecommendations cannot be satisfactorilyachieved, recourse must be made to theintegration of electric lighting with thedaylighting (see 4.3 below).

By providing good natural lighting,considerable energy savings can be made,but, as stated earlier, natural lighting isnot 'free'. Large areas of glazing canresult in considerable heat loss in winterand heat gain in summer, and can alsocause visual discomfort. These problemscan be successfully overcome if all aspectsof window performance are properly

considered early in the design process.This may mean including double glazingor one of the new glasses which have ahigh effective thermal insulation (whichcan also reduce noise interference fromthe exterior). Whilst many provisions,including blinds and sunshading devices,will increase the initial building cost, theyhave the potential of considerablyreducing running costs, and a balancedview needs to be taken.

The build-up of dirt on glazing willgradually reduce the amount of daylightentering an interior, and windows androoflights need regular cleaning: it mustbe easy to reach them or maintenance islikely to be poor or expensive. Experienceindicates that both surfaces of externalglazing should be cleaned at least once aterm, the frequency being greater indistricts which have a high level ofairborne dirt. (It should also beappreciated that children's work displayedon external glazing will reduce thedaylight in the room). Surfaces of roomswill also need regular cleaning andredecorating to maintain the level ofreflected light.

Note: In the past many schools havesuffered from poor environmentalconditions. It seemed that they had eitheran appropriate daylighting performanceand an uncomfortable thermalenvironment or vice versa. The reason forthis condition was usually a lack of anoverall design solution. It is important toremember that in this country the

ylighting and thermal conditions varyconsiderably throughout the year and thebuilding design needs to be able to takeaccount of these variations. For example,if a window is large enough to providesufficient light in winter together withacceptable view conditions, then it ispossible it may provide over-heating anddiscomfort glare in summer. To overcomethis possible problem, some form ofadjustable external sun-screening may benecessary as well as adequate naturalventilation. To minimise heat loss inwinter the window must have appropriatethermal insulation (U-value). Asmentioned earlier, this may well require


double glazing or one of the new glasseswhich minimise heat loss through the useof special coatings. It will also benecessary to ensure that the otherelements of the building, ie, the roof andwalls, minimise heat loss and heat gain. Itis important to stress that theenvironmental performance of thebuilding needs to be considered in anholistic way to ensure an acceptableperformance at all times.

4.1.2 Daylight QualityIn addition to providing the rightquantity of light, daylight can give to aninterior a particular unique character.Some of this is due to the variability ofthe daylight including sunlight: also, thedistribution of the light enhances thevisual field. The directional properties oflight from side windows (the 'flow oflight' across the room) are a significantattribute contributing to the modelling ofthe interior, including objects within itand surface textures, and providingbrightness to vertical surfaces, the amountdepending on the reflectance. Somevariability across room surfaces is alsoimportant (Fig 4).

It is recommended that the reflectanceof the wall surface finish should not beless than 0.6 because the effective wallreflectance will be reduced by thepresence of furniture and pin-up material.With regard to the ceiling, in order toenhance the daylit appearance of a space,the reflectance of the ceiling surface finishshould be as high as possible, and at least0.7.

4.1.3 GlareOne of the most important aspects ofobtaining a satisfactory interiorenvironment is to provide a balancedluminance distribution some contrastbut not excessive. If the luminance of thesky seen through a window is very highand close to the line of sight of a visualtask of much lower luminance, disabilityglare can occur due to a reduction in thetask contrast making details impossible tosee and thus reducing task performance.An example of disability glare can occurwhere there is a window in a wall on

19


Figure 20: Examples of glareand sun control, blinds may beeither opaque or translucent.

20

which there is a chalkboard: this shouldbe avoided.

Discomfort can be experienced whensome parts of an interior have a muchhigher luminance than the generalsurroundings: it may take some time tobecome apparent. Discomfort glare fromdaylight can be a more commonoccurrence than disability glare, andunder most circumstances its degree willdepend not on the window size or shape,but on the luminance of the sky seen inthe general direction of view. Datasuggests that for the UK an unprotectedwindow will be uncomfortably glaringover a significant period of the year. It hasbeen predicted that skies with an average

luminance exceeding 8900cd/m2(corresponding to a whole-sky illuminanceof 28000 hix) will cause discomfort glare,and in the UK these are experienced forabout 25% of the working year.

Some reduction in the sky glare can beachieved by reducing the contrastbetween the window and itssurroundings, for example, by the use ofsplayed light-coloured reveals orincreasing the brightness of the windowwall by increasing its reflectance, orlighting it from a window in an adjacentwall. Window frames should be as light incolour as possible, whether stained orpainted timber, or painted or integrallycoloured metal or plastic. However, the

DISCOMFORT GLARE AMEUORATED BY UGHT COLOURED FRAME AND WINDOW WALL

soffit shoulight in colo light coloured

ceiling helpsto lessen contrastwith sky

overhang 'outrigger louvre

FIXED EXTERNAL CONTROLS

venetian blind

PTA

curtain

1retractable angular retractable vertical

blind blind

FLEXIBLE EXTERNAL CONTROLS

Pid

PT1

2

roller blind concertina blind

FLEXIBLE INTERNAL CONTROLS

flr

reduction of the sky luminance is themajor consideration, and where this islikely to be a problem provision should bemade for blinds (eg, horizontal or verticallouvre blinds) or curtains, which can betranslucent or opaque and internal orexternal, or retractable screens, canopiesor awnings. Permanent features such asroof overhangs may also assist in thismatter. However, it has been shown thatin the UK, overhangs of more than300mm over windows serve little purposein terms of shading or improveddaylighting (see DfEE Building Bulletin79, Passive Solar Schools, A DesignGuide). If the underside of the overhangis light in colour, the penetration will beimproved and excessive contrast with thesky can be avoided (Fig 20).

Rooflights can cause discomfort glarefor most of the working year if the glazingcan be seen directly from normal viewingpositions at angles of less than 35° abovethe horizontal (Fig 21). The glare can beameliorated by using measures similar tothose for vertical windows (Fig 22).Contrast between the glazing and itssurroundings can be reduced by usingcoffers with high reflectance sides whichalso cut off the view of the direct sky andby setting the rooflight in a light-coloured ceiling. The luminance of thesky seen can be reduced by adjustableblinds, shades or louvres. The use of apermanent diffining panel to close in acoffer at ceiling level can provideunsatisfactory conditions: it may becomedifficult to appreciate that the source oflight is natural and the feeling of 'daylightcontact' may be lost, particularly if theexterior glazing material is also diffusing(see 4.1.5). Further, on dull days, there


will be a noticeable reduction in theamount of contributed light.

4.1.4 Sunlight ControlWhile most of the time sunlight isconsidered to be an amenity in thiscountry, there are occasions particularly inthe summer months when it is necessaryto provide some protection from itsinconveniences such as excessive direct

Figure 21: Rooflight glazingshould not be visible below acut-off angle of 350

Figure 22 Left: VictoriaInfants' School, SandwellM.B.C. Motorised perforatedmetal louvre blinds fitted torooflights over classrooms(see also Figure 13). [Photo:P. Locker, Photo GraphicDesign]Right: Netley Abbey Schoolshowing use of translucentroller blinds. [Photo: J. Low]

2 1

"r.* Kr%


Figure 23: Courtyard view.

22

heat and glare, and shading devices arerequired. These can usually be designedin conjunction with the devicesconsidered for the reduction of sky glare(see section 4.1.3).

It is not usual in the climate of thiscountry to design permanently fixedfeatures because they will reduce theamount of daylight entering the room atall times and this could be particularlyundesirable in the winter months.

The protection can be provided byadjustable screening devices such ascurtains and blinds including louvre blinds(Fig 22). For optimum sun protection,the solar control devices should be placedoutside the window: retractable screens,canopies or awnings can be used here (Fig20). It is important in designing asunlight control system that it takes intoaccount the extent of the use of theschool during the summer months.

4.1.5 Exterior Visual ContactIn addition to providing natural light, oneof the main properties of windows is theprovision of visual contact with theoutside. This avoids a feeling of enclosureand claustrophobia, and also providesvisual relaxation and a 'view'. Whereverpossible, the shape, size and disposition ofthe windows should be related to theview, and avoid any deprivation or

curtailment of it by their position, heightor width. A minimum glazed area of 20%of the internal elevation of the exteriorwall is recommended. Any seriousobstruction to the view can be annoyingand appropriate sill and head heights areimportant (Fig 9).

While the view out should preferablyhave close, middle and distantcomponents, and contain some naturalelements, frequently this is not possible,and a popular alternative is the use ofcourtyards. For these to be successful,they must be well maintained, preferablywith suitable landscaping and some viewsof the sky, and have an adequate viewdimension across the courtyard of not lessthan 10m.

In some instances, a reasonable view ofthe exterior may not be feasible, and inthese cases a long internal view is a usefuladdition within a large space or possiblythrough glazed partitions. However, it ispreferable to have a feeling of 'daylightcontact' maybe from rooflights andincluding atria (Fig 19).

On some occasions, a view out can bea disadvantage and cause distraction, andin these circumstances, blinds or curtainsshould be provided. In addition, there aresituations where there is a need forprivacy and here the view into a buildingneeds to be considered.

4.2 Electric LightingAs with natural lighting, the main aimsare concerned with:

function to enable tasks to beperformed accurately and comfortablyand to facilitate safe movement about thebuilding, and

amenity to light the interior of thebuilding in order to provide a pleasantand stimulating environment.

The values of illuminance quoted inthis document are given in terms of'Standard Maintained Illuminance' whichis the form of recommendation used bythe national and international lightinginstitutions. This is the minimumilluminance which should be provided atall times through the life of the installation.

The CIBSE Code for Interior Lighting,1994, 'Section 2.6.4.4 Public and educationbuildings' provides figures for a widerrange of specific interiors and activities.

An illuminance of 500 lux fordemanding tasks may be provided byusing local lighting to supplement general


lighting: under these circumstances, theilluminance on the surround area shouldideally not be less than one third of thatof the working area to avoid excessivecontrast and distraction.

Because of the special characteristics ofatria and in particular the spatial con-siderations, it is advised that anilluminance of not less than 400 lux witha high uniformity should be used for theseareas and in addition, light verticalsurfaces incorporating high reflectancevalues should be a feature of the design.The lighting of atria is discussed in moredetail in the illustrative example inAppendix 8.3.

Many rooms in educational buildings,and particularly spaces in primary schools,are used flexibly for a variety of purposeswithout very fixed work places. Thelighting arrangements must reflect thisrequirement and provision made bycontrols and particularly switchingfacilities to satisfy this flexibility.

Lamps and luminaires need to beregularly cleaned to minimise thedeterioration of their light outputperformance. To ensure this can happen

Standard Maintained

Illuminance

lux

Uniformity

Ratio

Limiting

Glare

Index

1. General Teaching 300 * 0.8 19

Spaces

2. Teaching Spaces

with close and

detailed work

500 * 0.8 19

(eg, art and craft rooms)

3. Circulation Spaces:

corridors, stairs

entrance halls, lobbies &

80 - 120 19

waiting areas 175 - 250 19

reception areas 250 - 350 19

4. Atria 400 * - 19

*Although particular illuminance values are quoted for the different areas, a small variation in

these values is unlikely to be a problem.

BEST COPY AVAILABLEtx:t

Table 6: Illuminance,Uniformity Ratio and LimitingGlare Index for schools.

23


24

with the minimum of fuss, it is necessaryto consider maintenance when selectingthe lighting equipment: luminaires whichrequire the use of special arrangementsfor cleaning and re-lamping should beavoided unless there is definite provisionfor this matter. The possibility ofinstalling an incorrect lamp can bereduced by keeping the number ofdifferent lamp types used in a building toa minimum. This particularly applies tofluorescent lamps where it is possible touse the wrong colour and with spot lampswhere it is necessary to ensure the correctbeam characteristics are used.

In a typical school, all electric lightingequipment should-be cleaned at leastonce a year. The cleaning should be moreoften in districts which are particularlydirty. As in the case of natural lighting,the level of reflected light needs to bemaintained by ensuring the room surfacesare kept clean and repainted regularly.

4.2.1 GlareDisability glare does not usually occurfrom electric lighting in ordinary interiorspaces, but discomfort glare caused byluminaires can be a problem. This iscontrolled by the luminance and size ofthe glare source, its position in the fieldof view and the visual adaptation given bythe background luminance. These factorswhen combined in the Glare EvaluationSystem described in CIBSE TechnicalMemorandum No. 10 produce a GlareIndex which should be below thespecified Limiting Glare Index forfreedom from discomfort glare. (Manymanufacturers publish tabular data fortheir luminaires which enables the GlareIndex information to be obtained fairlyquickly.)

There is a recent tendency to adoptluminaires with tightly controlleddownward light distributions in the beliefthat this will minimise direct glare,particularly in areas where VDUs are inuse. This is true for distant views of theluminaire but the student is often leftwith a bright light source directlyoverhead which can be disconcerting andcan make reading text printed on a glossysurface almost impossible. A luminaire in

30

which the lamps are not directly visiblefrom below may be preferable to avoidhigh luminance reflections on thehorizontal working plane.

Direct glare from a ceiling mountedluminaire depends on a number of factorsincluding the contrast between theluminaire and the ceiling surface. Withthe narrow downward distribution theonly light reaching the ceiling may bethat reflected from the work surfacesbelow and the contrast with the luminousarea of the luminaire may be high. Aluminaire, perhaps surface mounted orsuspended, depending on the ceilingheight, which emits light directly on tothe ceiling will reduce this contrast and bemore generally acceptable. Various typesof luminaires are detailed in Appendix 5.

4.2.2 Flicker and High FrequencyOperationElectric light sources, particularly somedischarge lamps, can frequently be seen toflicker, a problem that can causediscomfort or even annoyance to somepeople. This is caused at the cathode ofthe lamp and by oscillation in lightoutput which can also producestroboscopic effects with moving objects:these can be dangerous for example,rotating machinery in a workshop canappear to be stationary.

This phenomenon can usually beovercome by the use of luminaires withhigh frequency control gear. These donot remove the oscillation but raise therate to a very high level which is notperceived by humans. An additionaladvantage of using high frequency controlgear is the improved efficacy that can beobtained from the lamps.

4.2.3 Veiling ReflectionsHigh luminance reflections in a task arereferred to as veiling reflections, and canaffect task performance due to areduction in the task contrast and couldcause discomfort or distraction: the term'reflected glare' is sometimes used. Thetask detail or its background, or both, islikely to have some degree of specularity,and any high luminance source situated inthe offending zone will be specularly

reflected to the observer.Common examples of the veiling

reflection problem occur with VDUscreens, glossy paper and shiny instruments,and with windows or luminaires in theoffending zone (Figs 24 and 25).

Veiling reflections can be reduced byusing matt materials in the task area, byreducing the luminance in the offendingzone or by altering the geometry of thesituation so that the high luminance isnot in the offending zone.

4.2.4 Distribution of LightThe appearance of a space is controlled toa large extent by the distribution of lightwithin it. It is important that the wallsand ceiling receive light, ideally bothdirectly from the luminaires and byinter-reflection, and to ensure thishappens the selection of luminaires isimportant (see Appendix 5).

For a space to have an acceptableoverall lightness, it will be necessary touse relatively high surface reflectances, ie,wall finish reflectance not less than 0.6with a ceiling finish reflectance not lessthan 0.7 and a floor reflectance as high asis practicable. Glossy finishes to ceilingsand walls should be avoided to minimiseconfusing reflections and glare. (Note:since it is common practice for teachers touse the wall surfaces for display, a loweraverage wall reflectance value, eg, 0.30.5 will need to be used for calculations,


r

r 17>0./ 1_;_

e*

Figure 24: Veiling reflections,schematic diagram of'offending zone'.

Figure 25: Veiling reflectionson vertical and horizontalsurfaces.

Figure 26: Preferentiallighting of wall and displaysurfaces.

25


Figure 27: Examples of wall-washing luminaires which canbe used for preferentiallighting.

26

depending on the wall finish and theamount of display material.)

As with natural lighting, characterand interest can be given to the interiorif some directional light is introduced toprovide modelling and some variety isprovided by controlled visual contrastson the main surfaces. The preferentiallighting of some wall surfaces, usingspotlights which produce soft-edgedpools of light or wall-washing by tubularfluorescent lamps, is useful for thispurpose and, of course, lighting for thedisplay of particular items such as pupils'work can assist this process (Fig 26 and

27). It is suggested that the averagesupplementary illuminance on the wallsurface is at least 200 lux when thehorizontal reference plane illuminance is300 lux, and this should be scaled upwhen the horizontal plane illuminance is500 lux.

As stated earlier, the most effectiveelectric lighting designs are thosecomprising different elements whichcombine to make a successful lightinginstallation in terms of function andappearance - for example, generallighting, task lighting and accentlighting.

.,; 2

4.2.5 Choice of Lamp andLuminaireEnergy efficiency in electric lighting is amatter of selecting equipment whichproduces the lighting required in anenergy effective way, and which is onlyused when it is actually needed. This willrequire choosing lamps which have a highefficacy, ie, those lamps which providehigh levels of light for the energy theyconsume, and using luminaires whichhave high light outputs as well as controlsto provide electric lighting whichcomplements the natural lighting.

The choice of lamp will be dependenton a number of parameters, includingluminous efficacy, total light output (orwattage), colour rendering, colourappearance, life, size, need for controlgear, starting characteristics and, ofcourse, cost. Some typical characteristicsfor the types of lamp most suitable for usein schools are given in Appendix 3, andgreater detail can be obtained from themanufacturers.

While some properties includingefficacy and life are of paramountimportance in selecting the most efficientand economically acceptable scheme,much consideration has to be given inschools to the colour properties. Twocolour properties, related to the spectralcomposition of the emitted light, arenormally specified. One is colourappearance concerned with the apparentcolour of the light and is indicated by itsCorrelated Colour Temperature (CCT)and the other is colour renderingc..:ncerned with the effect the light has onthe colours of surfaces this is quantifiedby the CIE General Colour RenderingIndex (Ra). For practical purposes, CCTvalues and Ra values are groupedaccording to the descriptions given in thetable in Appendix 3. For schools, it issuggested that lamps with a Warm toIntermediate colour appearanceclassification are used. Warmer colouredlamps with a CCT 2800K 3000Kshould be used as accent lighting or inareas where a more domestic atmosphereis required. For installations where theelectric lighting supplements thedaylighting, it is suggested that lamps of


Intermediate CCT class of about 4000Kshould be used, wherever possible. Dueto the variations which occur in thecolour appearance of daylight, the barelamps should be screened from directview. To enable accurate colourjudgements to be made, it is suggestedthat lamps with an Ra of not less than 80(Group 1B) be used.

Small light sources enable the opticalcontrol to be more accurate but, for thesame output, will have a higher luminanceand are potentially more glaring andtherefore should be screened from normaldirections of view.

It should be noted that all dischargelamps require the use of control gear fortheir operation and that high pressuredischarge lamps have a time delay inreaching their full light output after beingswitched on and in re-striking after beingswitched off. The use of high frequencycontrol gear with fluorescent tubes willneed consideration in situations where theavoidance of flicker is important.

The choice of lamp and luminaire are,of course, interdependent and one cannotbe considered without reference to theother.

The main items to be examined in thechoice of luminaire are:

luminous efficiency and lightdistribution.

These are characterised by the LightOutput Ratio values (total, downwardand upward) and the shape of theluminous intensity distribution (polarcurve). These factors describe not onlythe amount of light falling on theworking plane but also that on the ceilingand walls a prime component indetermining the visual appearance of thespace. This light distribution data will alsoprovide information regarding thepossibility of glare being a problem. Thenominal spacing/mounting height ratiowill also have to be noted to achieve therecommended uniformity of illuminance.(Detailed photometric information can beobtained from the luminairemanufacturers: some typical characteristicsare given for guidance in Appendix 5).

(ii) appearance.The appearance of the luminaires,


Figure 28: New BradwellPriory Common First School.Milton Keynes. Suspendedlinear lighting system. [Photo:Bucks County Council].

Note: BS 4533 : Luminaires.Part 101 : 1990. Specificationfor general requirements andtests.Part 102 : 1990. Particularrequirements.

28

0

when lit and unlit, should complementthe general design of the interior. Thecontribution which the luminaires willmake to the character of the space willhave to be examined. Mounting position(ceiling recessed, surface mounted,suspended etc.) is very important in thisrespect (Fig 28).

(di) ease of maintenance.The luminaire design should, wherever

possible, avoid surfaces on which dust anddirt can be deposited. It should also allowmaintenance cleaning and re-lampingto be performed easily without the needfor a special procedure.Note: All lighting equipment shouldgenerally comply with the relevant BritishStandards and Euronorms or equivalent.

4.3 Integrated daylight andelectric lightWhen the daylight recommendationscannot be achieved throughout the space,a supplement of electric lighting can beprovided, but it is usual to require thespace to appear predominantly daylit.

The first requirement is for the electriclighting to supplement the daylight sothat the combined illuminance is suitablefor the task or activities being undertaken,and an effective use of controls isnecessary.

The other requirement is to achieve asatisfactory appearance by the balance of

1=1111U

0216-1

brightness throughout the space so thatsurfaces in parts remote from thewindows do not seem dim and gloomy.This can occur even when there istechnically enough light due to the visualadaptation caused by a relatively brightwindow. An appearance which is morevisually acceptable can be achieved bylighting preferentially the wall remotefrom the windows by 'building lighting'which is separate to that required for thetask. This wall lighting can be moreeffective when some variety isincorporated, as previously described(4.2.4). The ceiling will also need to bewell-lit.

The electrical distribution circuits andtheir switching arrangements should besuitably organised. In manycircumstances, the supplementary electriclight will have to be designed to operateseparately from the night-time electriclighting (see Appendix 6).

As mentioned earlier, it is advised thatthe lamps used for electric lighting in thistype of combined lighting should be ofIntermediate CCT class of about 4000K.The bare lamps should, wherever possible,be screened from direct view because ofthe variation which can occur in thecolour appearance of daylight.

With regard to the possibility ofdiscomfort glare for combined installationsand to ensure the degree of glare from

the two installations operating together isacceptable, it is advised that eachinstallation should be designed to beindependently within acceptable limits.

4.4 Aids to Lighting DesignIn this section, guidance is given ondaylighting, electric fighting and acombination of the two. This includesnumerical recommendations andtechniques. Whilst numerical values havetheir place, particularly regarding visualperformance and comfort, it is virtuallyimpossible to quantify the lit appearancein the same way. As an aid to developingthis aspect of design, it is helpful for thedesigner to use a number of techniques toenable design possibilities to be exploredand ultimately tested. These includeshaded perspectives and architecturalmodels, particularly for daylight andsunlight studies, and it is likely thatcomputer visualisation programs willbecome more common in the near future.

With regard to shaded perspectives,these can be used to develop the requiredlight pattern to identify the areas thatneed to be 'high lit' or to explore, in athree-dimensional way, the fightingperformance of a window/rooflightsystem. They are also particularly useful asa way of communicating design ideas.

Architectural models are commonlyused to explore daylighting designs. Forthis purpose it is advised that a scale ofnot less than 1:20 be used and that theyare made from materials that are opaqueand have the appropriate surfacereflectance and colour. It is obviouslyimportant that the models aredimensionally correct and that anyexternal obstructions are included. It isnot essential to model precisely windowdetails such as glazing bars or glazingmaterials, but these must be taken intoaccount if the model is used formeasurements. It is important to includeany permanent shading devices includingroof overhangs. The model can be used inthree ways, to appraise the appearance ofthe lit space, to measure the daylightdistribution and to examine the directsunlight penetration.

For the appearance appraisal it will be


necessary to provide viewing slots. Theseneed to be placed at a normal headposition and can be used under real orartificial sky conditions. It is of courseimportant that no stray light enters themodel through the viewing slot. It isoften easier and more convenient to use amodelscope either directly or with acamera.

When the model is to be used formeasuring the daylight distribution,usually under an overcast sky condition, itwill be necessary to provide entrypositions for small photocells, but it mustbe possible to seal these openings whenthe measurements are being made toavoid errors due to light leakage. It isuseful to measure not only the insidevalues but also an outside, unobstructed,sky value: which will enable themeasurements to be quoted in terms ofdaylight factor. The measurements can bemade under a real overcast sky, but it is

Figure 29: Use of model inartificial sky at the BuildingResearch Establishment,Garston.

,vwf

29


more convenient to use an artificial sky toovercome the problem of light levelvariability (Fig 29). The artificial sky is apiece of equipment which typically modelsthe CIE overcast sky condition usingmirrors and electric lamps and thereforeremains constant whilst the measurementsare made.

Models can also be used to test sunpenetration. In this case the model can beused in conjunction with a spot lamp torepresent the sun and a sundial to enablethe correct relationship between themodel and the spot light (artificial sun) tobe established. With this equipment arange of sun positions can be explored.An alternative is to use the model inconjunction with a heliodon, a piece of

Figure 30: Use of model inconjunction with a heliodon.

equipment that enables thesun/site/building relationship to beexplored more easily (Fig 30).

Whilst few design practices have theirown artificial sky or heliodon, these piecesof equipment are commonly available inSchools of Architecture, UniversityBuilding Departments and ResearchEstablishments.

Calculations for the determination ofpoint daylight factor, illuminance andluminance, have not been included in thispublication because they appear elsewhereand in particular the CIBSE Publications:Code for Interior Lighting 1994 andApplications Manual: Window Design1987.

3 6

30

Section 5: Lighting for particular applications

The discussion in the earlier parts of this documentapplies to all areas of a school. However, particularspaces may need additional attention due to theirspecialised requirements, some of which are morecommonly found in secondary schools.

Figure 31: Blenheim HighSchool, Epsom, Surrey, mainentrance. [Photo: P. Locker)

5.1 Circulation Areas.The circulation routes through a schoolare its main arteries taking pupils, staffand visitors from the main gate throughto the various particular areas. They needto be functional in that people need tofind their way easily and safely throughthe building, even when they areunfamiliar with it. These routes also needto be visually stimulating. Finally theyneed to provide means of escape and thismay require emergency lighting (seeSection 5.14).

5.1.1 Exterior circulation and themain entrance

During the daytime the route from themain gate to the main entrance willusually be obvious. This is because of thesite organisation and the architecturaltreatment of the main entrance. At night-time, however, things will be different.The main gate may need to be identified,perhaps with an illuminated sign, togetherwith a high-lit area around the gate. Thisarea then needs to be linked visually to

the main entrance of the school, whichwill mean lighting the walkway andvehicle routes. The important thing is tolight the pavement and road surfaces; itcan be done from a low height usingbollard type fittings or higher post-toplanterns, but the luminance in the normaldirections of view should be kept to aminimum. This is to avoid glare and tomaximise the visual effectiveness ofthe lighting.

To aid progress across the site, themain entrance needs to be bright andwelcoming. This can be achieved, if thefront of the main entrance is glazed, byhigh-lighting the vertical surfaces withinthe entrance area. These can also be usedfor student displays and the display ofschool trophies. The interior light in theentrance area will also spill out into thearea in front of the doorway making itinviting and helping to identify any steps.During daytime the entrance area shouldreceive a good level of daylightparticularly on vertical surfaces; however,if this is not possible then supplementaryelectric lighting may be necessary indisplay areas.

5.1.2 Corridors and stairs

The corridors and stairs are the mainelements of circulation and although theirprime purpose is to get people from oneplace to another, they are also an

731


important facility in identifying the workand character of the school. They shouldbe lit to provide safe movement aroundthe building and also to produceinteresting and, if possible, stimulatingspaces.The lighting, both natural andelectric, should aim to provide visualvariety and an enhancement of some areasrather than others. Different surface

Figure 32: Low energycorridor lighting with change ofluminaire and daylighting insitting area. Netherhall School,Cambridgeshire.[Photo: P. Locker]

Day lighting of staircase withcontrasting treads and risersand avoidance of glare fromwindows. [Photo: P. Locker]

32

materials and particularly differenttextures, can be useful in this respect.Again, the brightness of individualluminaires should be limited and they canpreferentially light walls and alcoves used

for sitting and display. In this instance, forsingle storey buildings, rooflights canmake a major contribution. Viewwindows which look out, or into someinternal spaces, can be valuable sources oforientation. The electric lighting can bewall or ceiling mounted but it needs to bean integrated part of the building.

Stairs need to be well lit to avoidaccidents. The main consideration is toprovide lighting which ensures that thestaircase treads and risers are well definedwith a contrast between the treads andthe risers and that the luminance patternis such that there are no problems fromglare. This means avoiding brightluminaires or windows in the normal fieldof view when using the staircase.

It is recommended that an averageilluminance of 80 120 lux be providedat floor level in corridors and stairs.Entrance halls, lobbies and waiting roomsrequire a higher illuminance of 175 250lux. Reception areas should be lit to 250350 lux (Fig 33). Downlighters are notrecommended over reception desks as thelack of a diffiise component of lightmakes lip-reading difficult (see 2.1)

Special attention must be given to theavoidance of glare and other visualproblems. For example, the positioning of

V IV,


a window at the end of a corridor can beannoying because of the silhouette visionit can cause and can be dangerous inproducing disability glare (Fig 34).

Interest and variety can be supplied incirculation areas by display and exhibitionspaces, possibly in alcoves, which arepreferentially lit (Fig 35). If private studyareas are provided off circulation routes,

they should have suitable local electriclighting, and ideally be near a window.

In primary schools, it is common forcirculation to be part of general teachingspaces and vice versa. This will require thedesigner to decide on the particularlighting needs of this type of space.Usually the more demanding task willtake priority.

Figure 33: Main foyer andreception area at BlenheimHigh School, Epsom, Surrey.[Photo: P. Locker]

Figure 34: The benefit of aside-lit corridor.

Windows at the end of a corridor showobjects in silhouette.

A side-lit corridor is preferable

33


Figure 35: Circulation streetwith activity areas. VictoriaInfants' School, SandwellM.B.C. [Photo: P. Locker]

5.1.3 Circulation/activity areas

Where areas cater for other activities aswell as circulation, lighting will need toconsider both functions. It will be helpfulif the circulation route, though part of anactivity area, can be separately identified.This may be achieved with changes in thelighting, but also changes in surfacecolour can be used. Another possibility isa change in ceiling height which can becombined with a change in lighting.Some recent designs have daylit 'streets'which are used for a wide range ofactivities and also form an importantfocus for the school. As with corridors,these areas often incorporate displays,which may be two or three dimensional,on vertical surfaces or free-standing.These benefit from accent lighting andtheir changing nature requires a degree offlexibility in the display lighting. This canbe achieved with a track lighting systemequipped with very low glare, adjustableluminaires.

.LAIVETE-1451!

34

liff'r'rrrrr

4 0

5.2 Areas with Display ScreenEquipmentDisplay Screen Equipment(DSE) is thename now given to Visual Display Units(VDUs) which have become increasinglyimportant items of teaching equipment inboth primary and secondary schools. Thevisual conditions and correct lighting fortheir satisfactory use need care andattention. DSE is generally found in usethroughout schools with small numbersof computers in all subject areas. Largernumbers of machines may be grouped inareas such as library resource areas andspecialist computer studies rooms.

One of the main problems encounteredconcerns the unwanted reflections whichcan occur in the screens of DSE. Thesecan be bright enough to make it difficultto read the screen characters, reducingthe contrast between them and the screenbackground. To control this situation, thelighting of the space in front of the screenmust be such that the luminance of anysurface is low enough not to interferewith the reading of the screen characters;changes in luminance must be gradual,and luminaires and windows having ahigh luminance in directions affecting thescreen must be avoided (Fig 25).

One obvious demonstration of thiseffect is the student's white shirt orblouse acting as a large luminous source,producing a reflection in the screen.Whether this is critical or not will dependon the luminance of the screen. Positivepolarity screens (eg, Windows basedprogrammes or screens with a white orlight coloured background) will haverelatively high brightness (70-100cd/m2)which will significantly reduce the effectof reflected images. Negative polarityscreens (DOS based programmes orscreens with a black or dark colouredbackground) will have relatively lowbrightness (2-8cd/m2) and reflections onthe screen will be relatively brighter whichcan make it difficult to see the datadisplayed. With positive polarity screensthere should be no problem but withnegative polarity screens some action maybe necessary. The students could beencouraged to wear darker clothing suchas pullovers or jackets where the problem

is greatest. Filters might prove useful inreducing the brightness and sharpness ofthe images and many screens are nowbeing produced with a matt surface whichwill reduce the sharpness of any reflectedimages. Fortunately the majority ofsoftware used in schools is of the Windowstype which produces a positive polaritydisplay on the screens. Allowance can bemade for screen brightness whenchoosing luminaires (see CIBSE LG3reference at end of section) but mostteaching spaces will only require to bedesigned for the use of high brightnessscreens. The 1996 edition of LG3quantifies the changes to the luminancelimiting value of a luminaire with respectto the type of software and the type ofscreen being used. In areas where DSE isused intensively, ie, computer rooms andlibrary resource areas, electric lightingschemes which have been found suitableemploy ceiling mounted luminaires whichhave a louvre type optical control systemwith low luminance above defined criticalangles. Another possibility is indirectlighting or uplighting; this technique hasthe benefit of not normally creating highluminance within the offending zone. Inappearance terms, a combination of bothsystems is preferable.

The combination of direct and indirectlighting offers a number of advantagesover either direct or indirect only. Wheresuspended luminaires can be used (due tofloor to ceiling heights greater than 3.0m)the uplighting element will increase thebackground surface brightness, reducingthe contrast between it and the directlighting element. By reducing thecontrast it is possible to consider a lessonerous luminaire distribution. Forexample a Category 3 louvre, as describedin CIBSE publication LG3, might bereplaced with a non-Category louvre.Surface mounted luminaires can alsoprovide some light onto the ceiling butrecessed type luminaires generally do not.

These techniques have been widelyused in commercial premises where thespaces and rooms can be large.

In schools where classrooms aregenerally small in comparison with openplan offices it is much more important to


consider the geometry of spacescontaining computers. Relatively smallrooms or those with high ceilings (morethan 3.5m) may not need any specialtreatment other than good classroomlighting, as the luminaire mountingheight may not cause any images in thescreen. Simple changes in layout ofequipment might also be sufficient toreduce bright images.

In most teaching spaces the number ofcomputers in use is small and the maindesign consideration should be work onthe horizontal plane. This includesreading, writing and practical activities.Louvre type fittings designed to reduceglare on vertical screens may still producehigh luminance reflections on thehorizontal plane which can make workingon reflective materials very difficult. Thiscan be a problem when reading glossybooks, working on metal objects etc(Figures 24 and 25). Reflections are aparticular problem for the visuallyimpaired.

There is a tendency to specify louvretype fittings in all spaces because DSE isused to support teaching in any subjectarea. This is not necessary considering thesmall number of computers in mostspaces and the simplicity of moving thescreens to avoid glare from luminaires,the short periods for which computers arein use and the high brightness of Windowsbased programmes which are now in usealmost everywhere.

There is no substitute for goodclassroom lighting design.

One element that should always beconsidered is the distribution of light toensure that the vertical surfaces within theroom are adequately lit. This may involveusing two or three lighting installations inthe same space in order that a satisfactorybalance of light is achieved.

Some control over the illuminance, inrooms specially used for computing, maybe considered desirable, so that theexcessive initial illuminances do not causeproblems to the user. Dimmable highfrequency fluorescent luminaires may beconsidered necessary in thesecircumstances. These are more expensivethan normal luminaires but will provide

35


Figure 36: Sciencelaboratory, Dr Challenor's BoysGrammar School, Amersham.[Photo: Bucks County Council)

36

better conditions, especially where theusers are in the classroom for a long time(eg, double periods, or longer).

Windows are usually the biggestfighting problems encountered in areascontaining DSE because of their relativelylarge size and high brightness. However,room layout can usually avoid placingcomputers where windows are visible tocomputer users as high luminance glaresources. Windows can also be screenedusing one of the devices discussed earlierfor the control of sun and sky glare.

A wide range of luminances in thegeneral field of view when using DSE cancause visual adaptation problems. Theconsequences can be a reduction in taskperformance and visual distraction,discomfort or even disability. Thecontributing luminances are concernedwith the display screen, the keyboard,objects such as documents on the desk,and with the background, particularly theimmediate background to the screen. Anunfortunate common example of the lastitem occurs when a display screen is seenagainst a window. Measures to restrict thisluminance range must be taken bycontrolling the distribution of the lightand the position and reflecting properties

of the components.DSE is often used by an individual for

a relatively short time (for example, tofind one item of information), and theproblems mentioned are tolerated.However, for more extended work, thevisual conditions become important forsatisfactory, comfortable use. Detailedguidance is given in CIBSE LightingGuide LG3 1996: The visual environmentfor display screen use.

5.3 Science Work andLaboratoriesFor primary schools this type of activitywill usually take place in general teachingareas, and the recommendations for thoseareas will usually suffice but the designershould check that there are no unusualrequirements. For the secondary schoollaboratory where intricate tasks areundertaken which need accurate readingsand subtle observations, higherilluminance may be appropriate. This canbe provided by general fighting (Fig 36)or by local task fighting supplementingthe general fighting.

Where fixed benching is used,adjustable bench lights are suitable,particularly where directional fighting is

r

appropriate, but they must be controlledso that they do not cause distraction orglare to neighbouring work positions orbecome a physical encumbrance.

Visual conditions can be made morecomfortable if the bench tops are made ofa material which is light rather than darkin colour and has a reasonably mattsurface to avoid awkward specularreflections. Advice regarding the finishesof tables etc, can be obtained from BritishStandard, BS 5873: Part 1 1980,Educational Furniture.

Demonstration benches may benefitfrom some preferential and directionallighting.

Many of the considerations forlaboratories also apply to preparationrooms associated with the laboratories.

Good lighting is particularly importantfor the users of laboratory areas to avoidaccidents and to ensure the safe handlingof equipment.

5.4 Design and Technology Roomsand WorkshopsAs with other situations where detailedwork is done, the lighting of areas fordesign and technology can mostconveniently be achieved bysupplementing the general lighting withlocal individual lighting which can beadjusted to suit the particular task,especially where directionality of the lightis important but provision must be madeto avoid interference to the workpositions and machines and those nearby.For lathes and other machine tools, locallights are often provided on the machines.For safety reasons, these must be on anextra low voltage supply. All luminairesshould be robust and it may be necessaryto protect the lamps with wire meshguards. They should be easily maintainedand cleaned at least once a term becausesuch spaces are often environmentallydirty.

A particular hazard, mentioned earlier,can occur with discharge lamps lightingmachinery with rotating parts as it may bedifficult to assess the speed of rotationdue to the stroboscopic effect. This canbe avoided by wiring alternate luminaireson different phases of the electrical supply

D p'


(not usually recommended as it increaseshazards during electrical maintenance), orby using high frequency control gear.

In Design and Technology areas it isoften desirable to have a display space forcompleted work, and this should bepreferentially lit. As with laboratoryspaces, some preferential lighting may berequired for demonstration areas.

It is particularly important for people inthese areas to have good lighting to avoidaccidents and to enable tools andequipment to be used safely. Goodrendering of colours is very important andlamps of CIE colour rendering group 1Bshould be used.

5.5 LibrariesThe lighting of library spaces must be co-ordinated to fulfil a number of functionsgeneral ambient lighting, lighting forvertical bookstacks, lighting for study andlighting for browsing. It is important thatthe lighting arrangements are designed sothat there is no conflict between theappearance of the different parts of theinstallation or with the light distributionthroughout the space (Fig 37). Particularattention needs to be given to theavoidance of problems with veilingreflections, with glare and with the use ofVDUs (see previous sections).

Ambient lighting from overheadluminaires can be used for general reading

Reference:

BS 5873 :Educational Furniture.

Part 1 : 1980. Specificationfor functional dimensions,identification and finish ofchairs and tables foreducational institutions.

Figure 37: Library withbookstacks and study area.Netherhall School, Cambridge.

437


Figure 38: Lighting ofbookstacks.

38

tables and browsing, but, due to itsdistribution characteristics, this arrange-ment is generally not ideal for verticalbookstacks as the illuminance level willusually be low, particularly for the bottomshelves. The vertical spines of books onthe stacks need to be lit by special means,and using luminaires with an asymmetricdistribution. Increased illuminance for thelower shelves can be obtained by the useof a light-coloured floor covering or byinclining them outwards. If it is notpossible to provide ceiling mountedlighting directly related to the bookstacks

due to the need for flexibility inbookstack position, it is suggested that acontinuous line or lines of luminaires beused and positioned at right angles to theline of the bookstacks (Fig 38). The typeof luminaire and its spacing will need tobe selected to provide an even illuminanceover the vertical spines of the books.More detailed information is given inCIBSE Lighting Guide: Libraries.Supplementary lighting should beprovided for study tables and carrels andfor the issue control desk. It may also benecessary to provide accent lighting forspecial displays.

Individual luminaires attached to thebookstacks or overhead luminaires incontinuous rows at right angles tobookstacks, allows bookstacks to be moved.

5.6 Art RoomsThe main requirement is good generallighting with artificial lighting at aboutthe 500 lux level. There are frequentpreferences for daylight from north-facingwindows and for the availability of strong,directional lighting (Fig 39), particularlyfor sculpture and work involving texture.At times, the entry of sunlight can be anadvantage, but windows associated withthis entry must be fitted with adjustablesun-screening devices. Good rendering ofcolours is very important and lamps ofCIE colour rendering group 1B shouldbe used. Some additional flexible lightingfor the display of work is desirable.

5.7 Sports Halls and GymnasiaAlthough it is generally considered thatdaylight is beneficial in sports halls andgymnasia, windows and rooflights arefrequently excluded because the sun andsky can cause both disability anddiscomfort glare to users who are movingquickly and often with an upward field ofview. Reflected glare from shiny surfacesand particularly floors can also be anuisance. If daylight apertures areprovided, screening facilities for use whennecessary should be available. To enhancethe visual environment, it is suggested thatluminaires with both upward anddownward light should be utilised. Thereshould be some control to keep glare to a

4 4

minimum and the light distributionshould provide adequate light on verticalsurfaces.

Lamps and luminaires should have wireguards or other impact-resistant protection.

Sports halls and gymnasia in schoolsare often used for non-sporting eventsincluding examinations, and thereforeadequate consideration must be given tothe lighting required for these events,some supplementary arrangement beinginstalled if necessary (see section 5.8).

Because of the high mounting of theluminaires, satisfactory maintenance ofthe lighting installation will be difficultunless special provision in the form ofaccess facilities is made. The use of long-fife lamps in these circumstances shouldbe examined.

Reference should be made to theCIBSE Lighting Guide LG4: Sports.

See also BRE General InformationReport 35: Daylighting for sports halls,Two case studies.

II 111!).


Figure 39: Directional light inan art room.

Figure 40: Sports Hall atOakmead School,Bournemouth, fitted withoccupancy controls to switchon lights only in parts of thehall which are in use.[Photo: Ex-Or Limited]

V

BESIC *PY AVAiLA LE39


Figure 41: left: Hall atWinton School, Andover.[Photo: Peter Cook]Right Drama Space atCambridge Regional College:daylight with black out.Bernard Stilwell Architects.[Photo: Jeremy Cockayne]

5.8 General Purpose Halls(Examination, assembly, performancesand PE) and drama & dance studiosVery often there will be a need for a largespace within the school to cater foractivities ranging from examination todrama (Fig 41). The design will dependon the range of activities. Blackout willalmost certainly be required as will adegree of flexibility in the lightingdependent on the range of uses envisagedand the budget. If the budget is limiteda general lighting installation ofluminaires which provide both upwardand downward light should be used. Theinstallation should meet the moststringent requirements in terms ofactivity, allowing the luminaires to beswitched in groups to provide someflexibility. To complement thisinstallation there should be a system ofelectric wiring which allowssupplementary lighting equipment to beinstalled when needed. This may be of astage lighting type which can be easilyhired when required.

For teaching of GCSE and A-level Dramaand theatre studies courses a goodstandard of stage and drama studiolighting will be required (see typical planson the following page).

In halls likely to be used for concerts,theatrical and dance productions it maybe necessary to arrange for an adaptablestage lighting system to be installed sothat each event can be appropriately lit.Lighting barrels will need to be placedabove the stage and in front of it so thatstage lights can be positioned to light thefaces of people performing on all areas ofthe stage. To achieve this, lighting needsto come from about 450 above and 450to either side of any position on stage.This may involve using wall mountedbrackets and lighting sockets. Wherethere is a fixed stage, floor-traps withstage lighting sockets should be locatedon either side for side-lighting dance, andfor special effects lighting.

High level, wall mounted and stagesockets should all be wired back to adimmer panel on one side of the stage.

-

404 6

FLOOR TRAP WITHSOCKETS ON STAGE

(if fixed stage)

DIMMER RACKS

SOCKET FOR CONTROL

DESK FOR SETTINGUP UGHTING

POSSIBLEPROSCENIUM

ARCH LOCATION

WALL BRACKETS

HIGH UP ON WALL

(STAGE MAY BE WHOLE WIDTH OFHALL OR BE PLATFORM ONLY)

SOCKET FORCONTROL BOARD

DURINGPERFORMANCE

For larger halls there may be a need toprovide a patch panel so that perhapsthirty individually wired sockets can bepatched into eighteen or twenty-fourdimmer ways. Control sockets for amobile control desk should be positionednear dimmer racks for setting-up the stagefighting and at the back of the hall forcontrolling the fighting during aproduction.

Drama and dance studios are usedprimarily for the teaching of drama withsome need for small dance class use.Whilst windows and daylight are of use,during lessons full blackout facilities willbe needed on all windows.

Drama lessons are used to teach groupskills, focusing on social and personaldevelopment, where general moodfighting across the whole studio isneeded, as well as performance and stagecraft skills, such as set and fighting design,where full theatre fighting is needed forperformance use in any area of the room.

To achieve this there needs to be abasic structure of fighting points acrossthe space for locating lights in any part ofthe room. Often the most convenientsolution is to place a series of pre-wiredfighting barrels at intervals across thewidth of the room. The fighting socketsshould all be wired back to a dimmerpanel and eighteen way control desklocated in one corner of the room.

BEST Copy MIA LE

REAR STAGE

BARREL FOR

BACK UGHT1NG

FRONT STAGE BARREL

(Deep stages mayneed one or moreintermediatebarrels)

FRONT OF HOUSEBARREL NEEDED

TO UGHT THOSEON FORE STAGE


PRE-VARED UGHTINGBARRELS ACROSS

WHOLE ROOM

WINDOWS SHOULDHAVE FULL BLACK-

OUT FACILITIES

SOUND AND UGHTCONTROL DESK

5.9 The Lighting of ChalkboardsIt is essential to light chalkboards so thatthe material on them can be seen easilyand comfortably by all members of theclass. (The term chalkboard here includesblackboards used with chalk andwhiteboards used with marker pens.) Oneof the frequent problems which occurs iscaused by bright veiling reflections in thechalkboard of luminaires or windows.While it may be difficult to reducesufficiently the luminance of thesesources, the problem can be appreciablyalleviated by having the chalkboardsurface as matt as possible. A blackboardneed not be black, but to retain asatisfactory contrast for the chalk writing,

STORAGE FOR UGHTINGAND OTHER EQUIPMENT

Left: Stage lighting of generalpurpose hall

Right: Stage lighting of adrama studio

Figure 42: Chalkboardlighting

Chalkboard luminaire must be installed within theshaded triangle, to avoid reflections in the board tothe nearest viewer

4 7 41


References:

(1) Building Bulletin 87:Guidelines for EnvironmentalDesign in Schools, DfEE,ISBN 0 11 271013 1,The Stationery Office 1997

(2) RNIB/GBDA Joint MobilityUnit, 224 Great PortlandStreet, London W1N 6AATel: 0171 388 1266Fax 0171 388 3160

(3) The Partially SightedSociety, 62 Salusbury Road,London NW6 6N5Tel: 0171 372 155119/3/97 revision

(4) Building Sight, PeterBarker, Jon Barrick, RodWilson, RNIB, ISBN 011 701993 3, HMSO 1995, £35

42

its surface reflectance should not begreater than 0.1. A window in the samewall as a chalkboard should be avoidedbecause there could be disability glare forthe class producing severe difficulties inseeing the material on the chalkboard.

The chalkboard should be litpreferentially and a ceiling-mountedluminaire shielded from the direct view ofthe class is suitable (special luminaires areavailable commercially). The luminaireshould be positioned as much as possibleabove and in front of the chalkboard butsuch that veiling reflections to the frontof the class are avoided (Fig 42). Theuniformity over the whole board surfaceshould be as high as possible with littlespill light around it. The recommendedaverage illuminance over the surface is500 lux, but this can be halved in the caseof whiteboards.

5.10 Lighting and Visual AidsVisual aids are commonly used forteaching, particularly film, slide andoverhead projectors as well as televisionand video equipment. For the use ofthese teaching aids it is necessary toprovide a lower level of lighting so thatthe presentation can be seen comfortablyand clearly. For film and slide use, naturallight must be excluded with suitableblack-out facilities. Curtains and normalwindow blinds are usually not adequate;ideally black-out blinds which fit intoslots surrounding the window revealsshould be used. Sufficient light should beprovided to enable notes to be takenduring the presentation, and an illuminanceover the seating areas within the range15-30 lux is suitable. It is important thatthis should be provided by luminaireswhich have no lit element within thenormal field of view. The reason for this isthat if there are self-luminous elementswithin the field of view under theseconditions, they will make the viewing ofthe presentation difficult. Also, lightshould not fall on to the projection screenand it should not be possible to seereflected images of luminaires or windowson the screen surface of televisionmonitors. (See also Appendix 6 for detailsregarding lighting controls).

v.,

5.11 Lighting for pupils with visualand hearing impairments

Lighting and acoustic criteria are veryimportant both to the visually impairedand to the hearing impaired. If onesensory channel is impaired more relianceis placed on the other channel. Forexample, the use of aural cues by thevisually impaired and lip-reading by thehearing impaired. (See Building Bulletin87(1) for advice on acoustic criteria forthe hearing impaired).

The design of specialistaccommodation for the visually impairedis beyond the scope of this document andexpert advice should be sought(2,3).

The move towards integration of pupilswith special educational needs intomainstream schools means that there aresome measures that should be consideredin the initial design brief of all schools.Whilst there is some specialaccommodation in mainstream schools,for the most part those with visualimpairments are taught alongside theirpeers in ordinary classrooms. Therefore,all schools may have to cater for acontinuum from pupils with quite minorvisual impairments to those who areeducationally blind. Although pupils withvisual impairment are a minority they willbe present in most sixth forms.

Many of the low cost or no costmeasures can be applied to existingbuildings such as the choice of decor (seeUse of colour on page 43), tactilesurfaces and types of luminaires. For adetailed description of possible measuressee Building Sight published by theRNIB(4).

Other measures, such as providing orfacilitating the use of visual aids can beconsidered as necessary. There is no singlesolution and what may assist one personmay well not assist another. The followingnotes are offered as a general guide andshould help in the majority of cases.

Types of visual impairmentIt is useful for the designer to have ageneral understanding of the problemswith which the student may have to deal.Visual impairments can be put into two

4S rn r

broad classifications resulting from a widerange of clinical conditions.

1. Field defectsFirstly, there are conditions where what isseen is seen clearly but the visual field isrestricted. It may be that only the centralpart of the field is seen (tunnel vision)which can result from advanced glaucomaor some forms of retinitis pigmentosa. Inthis case mobility would be impairedalthough reading and the ability to dofine work would be largely unaffected.

The converse, loss of central vision,which might result from juvenile maculardegeneration, would mean thatmovement could be made in safety butthe ability to perform detailed tasks suchas reading or sewing would be extremelydifficult if not impossible.

Vision can be lost in 'patches', oftenresulting from diabetes, which maychange in size and position with time.There can also be the loss of one half ofthe visual field, either the right or leftside, or the upper or lower portion.

In all types of field defect the quantityof task illumination is generallyunimportant providing normalrecommendations are followed. Glareshould be avoided (see section on acuitybelow). Decor can help rapid orientation(see section on use of colour below).

2. AcuityThe other main condition is a loss ofacuity or a blurring of vision. The extentof the blurring varies widely from personto person and some may have to bringobjects and print extremely close to theireyes to see best. There may also be anassociated loss of colour vision.

Large print will, and higher illuminancemay, be of assistance depending upon thecause of the loss of acuity. Many schoolsnow have the facility to produce theirown reading material and the use of asans serif font of at least 14pt size can bea useful aid.

The effects of low acuity can beaggravated by glare, by which is meantany source of light or its reflection whichis much brighter than the level to whichthe individual is adapted, and this should

"


be avoided. A 'white' board on a darkcoloured wall can be a glare sourcewhereas a traditional 'blackboard' wouldnot. Similarly, a view of a daylit scenethrough a window can be a disabling glaresource.

Both loss of field and loss of acuity canoccur together and, even when causes aresimilar, the particular difficulties whichpeople with visual impairment experience,and their responses to light and otherenvironmental features, can vary widely.

The use of higher than normal taskilluminances can be of help to thosewhose acuity can be improved by thecontraction of the iris, producing a greaterdepth of field. In some cases, however,such as those with central corneaopacities, the iris needs to be dilated sothat the student sees 'around' the opacity.In such a case more light will aggravate,not relieve, the condition.

PositioningIn the past, many difficulties were causedby not realising the problems of thevisually impaired. It should not benecessary to say that students with visualimpairment should be seated where theycan best see the work in progress. Thismay mean a position outside the normalarrangement, eg, immediately in front ofthe teacher or board.

It is also important that any visual aidsare readily available for use. These mayrange from hand-held or stand mountedoptical magnifiers to CCTV magnifiers.Local lighting may also be used as an aid(see Local task lighting on page 45).

It may also be necessary to allow thestudent to change position within theteaching space to accommodate access toan electrical supply, cope with excessdaylight or use any other aid that isavailable.

Use of colourA carefully designed colour scheme can beof great help in recognising andidentifying a location and often more canbe done with coloured surfaces to aid thevisually impaired than with elaboratelighting installations. While in somespaces orientation may be established by

43


References:

(5) A design guide for the useof colour and contrast toimprove the built environmentfor visually impaired people,ICI, 1997, £15, obtainablefrom Du lux Technical Group,CI Paints, Wexham Road,Slough, SL2 5DSTel: 01753 691690

(6) Colour, Contrast andPerception - Design Guidancefor Internal Built Environments,£14.95 from Wayne CollinsAssociates,171-177 Great PortlandStreet, London, W1N 6NY.Tel: 0171 470 0202

Further information from:The University of ReadingResearch Group forNon-HandicappingEnvironments, Department ofConstruction Management andEngineering, P.O. Box 219,Whiteknights, Reading,RG6 6AW.Tel: 0118 931 6734

the furniture arrangement or by windowsduring daylight hours, in others it can beaided by the colour scheme. Whatevermethod is used, it is best adhered tothroughout the building, ie, the differentwall is always to the same side of the mainexit from the space.

Some visual impairments involve adegree of colour blindness and it isimportant that contrast should beintroduced in luminance and not justcolour. For example, pale green and palecream may be clearly distinguished by thenormally sighted but be seen as a singleshade of grey even by some pupils wherean impairment has not been identified.

Contrast in the decor should be usedto aid orientation within a space. Thevisually impaired primarily use sufficientlydifferentiated large surface areas toorientate themselves in a space particularlywhen it is unfamiliar. It may therefore beworth providing contrast between criticallarge surfaces such as ceiling, wall, floorand doors (5,6).

Special features such as stair nosings,handrails, door handles, the vertical edgesof doors, electrical switches and controlbuttons need to be highlighted by abigger colour difference to differentiatethem from the surrounding large surfaceareas. For instance, using a darker colourfor a handle which clearly contrasts withthe surface of the door will indicate whichway it swings. Coloured backplates toelectrical socket outlets and light switchesare available. They should also be locatedat constant heights throughout thebuilding and be within easy reach.

Strong contrast is also needed forgeneral obstacles particularly if theyprotrude at high level such as telephonebooths, literature displays and coat andhat stands.

Finally, high gloss finishes should beused with care as they can appear as glaresources when they reflect bright lightssuch as sunlight. In general, eggshellfinishes are to be preferred as somedirectional reflection is desirable ratherthan dead matt surfaces which may bedifficult to place precisely.

Changes in the tactile qualities ofsurfaces can also be useful to reinforce

" BEST COPY AVAILABLE

visual contrasts. They are most importantin schools for the blind.

DaylightThe fenestration will have been designedto facilitate the penetration of daylightwhich will be available for the majority ofnormal school hours. The window wallshould be light in colour, to reducecontrast with the outdoor scene, andwindow reveals may be splayed to increasethe apparent size of the glazing. It isimportant that students should be allowedto position themselves to use daylight totheir advantage rather than be constrainedto a formal classroom positioning.

Sunlight can be either a help or ahindrance, depending on the type ofvisual impairment, and some means ofcontrolling the quantity should beprovided. Traditionally this has been bymeans of blinds, either horizontal orvertical; both are successful but propermaintenance is necessary to ensure theircontinuing effectiveness.

It should be remembered that in theUK the greatest problems, both visualand thermal, are caused by low altitudesunlight at either end of the school day.Any solar shading devices, including thosefor rooflights must, therefore, be readilyadjustable to cater for a range ofconditions. Adjustment of solar shadingshould preferably be at the discretion ofthe students and not the teaching staffwho may not fully appreciate the visualdifficulties of the students.

Rooflights allow the ingress of sunlightover long periods therefore their designand positioning requires carefulconsideration to prevent obstruction ofthe sunlight by neighbouring buildingsand to eliminate glare (see page 21).

Electric lightThe control of glare from overheadlighting is particularly important tostudents with a visual impairment.

High frequency electronic ballasts forfluorescent lamps are to be preferred asthey are more efficient, and they avoidthe subliminal flicker that has been shownin scientific studies to increase headaches.Electronic ballasts also eliminate the

50

annoying visible flicker that conventionallyballasted lamps can demonstrate at theend of their life. If high frequency ballastsare used, consideration should be given tousing a regulated version which can bedimmed to allow the illuminance level tobe adjusted to suit the individual as wellas to save energy. The additional cost forthis is usually modest. It is important thatthe dimming circuit does not introduceadditional flicker.

It is not normally economic to installmore than the recommended illuminanceson the off-chance that they will be usefulsome day to a hypothetical visuallyimpaired student but additionalilluminance can often be readily suppliedwhen the need arises from local tasklighting luminaires.

SummaryProvide contrast in the decor to aid

orientation and the location of doors,door-handles, switches and socket outlets,changes in direction in corridors, changesin floor level, stairs and steps.

Avoid glare from windows, rooflightsand luminaires either distant orimmediately overhead.

Provide facilities for the use of anyvisual aids, eg, magnifiers, telescopes, etc.

Provide additional illumination byadjustable local task lighting as needed.

5.12 Local task lightingLocal task lighting is best provided fromadjustable reading luminaires usingcompact fluorescent lamps. These havethe advantage of long life and low energyconsumption leading to low operatingtemperatures, thus avoiding thermaldiscomfort when used close to the taskand the student.

Such luminaires can be positioned toprovide the directional characteristics andilluminance best suited to the student.Luminaires should have a heavy base toaid stability or be clamped to the desk,and the heads should be adjustable in allplanes so that they can be optimallypositioned. Note that it is possible for alocal lighting unit to cause glare toadjacent students but this can usually beavoided by careful siting.


A problem with local task lighting isthe need for an electrical supply which, ifonly wall or floor mounted supply socketoutlets are available, may introduce thehazards of trailing leads. If the studentcannot be positioned close to a socketthere is no simple solution to theproblem. An overhead supply wouldenable leads to be dropped down to thedesk position but it is hardly likely to beinstalled on a speculative basis. Batterypowered reading lights are also apossibility.

5.13 Exterior LightingThe exterior lighting of a school can servethree main functions. The first isconcerned with ensuring that pedestriansand those travelling by car or bicycle, cansee sufficiently well to enable them tomove safely from the street to theentrance of the school. This will require asystem of roadway/pathway lightingwhich will not only light these surfaces,but also provide sufficient verticalilluminance so that people and cars can beseen. It will be beneficial if the immediatesurrounding areas also receive some lightto define the general area. The schoolentrance will also need to be lit eitherinternally or externally so that it can beclearly identified. If car parking isprovided on the site this may also requirea system of area lighting.

The illuminance chosen should reflectthe location eg, urban or ruralenvironment, and the level of risk fromvandalism. The higher the risk, the higherthe illuminance and the larger the areathat should be covered.

The second function is concerned withthe appearance and security of the schoolbuildings at night (Fig 31). If a modicumof floodlighting can be provided it willshow the importance of the school withinthe community. Two stage securitylighting can be very effective. The firststage would be to provide a low level ofbackground lighting, just above theambient level, to deter opportunistvandals and to enhance the night-timeappearance of the school. This is combinedwith second stage floodlighting ofstrategic areas such as entrances and

52.45


References:

7. CIBSE Lighting Guide LG6Outdoor Environment.

8. The Institution of LightingEngineers, Guidance notes forthe reduction of light pollution,1994, available from ILE,Lennox House, 9 LawfordRoad, Rugby, Warwickshire,CV21 2DZ.

Figure 43: Lighting offootpath with a luminaire whichprojects light in a downwarddirection. [Photo: P. Locker)

BIEST COPY AVAILABLE

46

footpaths which is brought on by intruderdetectors. High intensity tungstenhalogen floodlights can be used for thissecond stage lighting. It should beremembered that security lighting is onlyof benefit where the building is undersurveillance from neighbours or passers-by or by a CCTV system. TheDepartment's Building Bulletin 78Security Lighting and the new buildingbulletin to be published in 1999 Securityby Design give further guidance onsecurity lighting and CCTV systems. Thechoice of light source is most criticalwhen designing for CCTV. The mostenergy efficient light source, low pressuresodium (SOX), is not suited to colourCCTV installations as it is mono-chromaticwith little or no colour renderingproperties and the narrow spectrum ofthe light does not match the spectralresponse of the cameras available.However an adequate picture may still bepossible, particularly with a black andwhite camera.

The third function of exterior lightingis the lighting of sports facilities such asplaying fields, tennis courts etc. Obviouslythe provision of this kind of lightingneeds to be justified, and if by installing

sports floodlighting the facilities can beused more extensively, perhaps the schoolcan obtain revenue by hiring out thesefacilities, enabling some of the capital costto be recovered.

It is not possible to describe here indetail the techniques of designingexterior lighting. The aim is to indicatepossibilities which should be consideredand if it is decided to include these formsof lighting then further information canbe obtained from the CIBSE publicationsreferring to outdoor lighting7 andsports lighting.

Aspects of exterior lighting which needspecial attention are: the avoidance oflight trespass, which is light causing anuisance to people and dwellings inneighbouring areas; and light pollutionwhich affects the local environment andatmosphere. Light trespass can becontrolled by suitable selection of thelight distribution of the luminaires toavoid 'spill light' and careful aiming offloodlights with the use of shieldsif necessary.

Generally the intensity of a floodlightbeam diminishes away from the centre. Inorder to control glare from light it is oftennecessary to refer to an outer beam wherethe intensity of the light has fallen to1/10th of the intensity of the main beam.

To prevent light pollution, luminairesmust be chosen with a light distributionwhere all the light from this outer beamfalls below an angle of 70° from thedownward vertical. These are called full-cut lanterns and usually require flat glasses.(see Fig 43).

To achieve the correct uniformity incar parks or playing fields higher columnsor closer spacing may be required.

VVhilst there is no legislationconcerning light pollution it has becomea major planning issue with localauthorities and some have adoptedstandards which define acceptable levelsof light pollution8. Planning Departmentsoften turn down proposals which wouldintroduce major new light sources intoareas without bright lights and wouldcreate substantial sky glow.

External lighting without automaticcontrol is not energy efficient. Some form

&) 4,

of automatic control should be provided.Control can be by photocells andtimeswitches or passive infra-red or otherintruder detectors.

Although the purpose of exteriorlighting equipment is to provideillumination at night, its daytimeappearance should not be overlooked andit should complement the appearance ofthe building and its landscape.

5.14 Emergency LightingThe purpose of emergency lighting is toprovide sufficient illumination in theevent of a failure of the electricity supplyto the normal electric lighting to enablethe building to be evacuated quickly andsafely and to control securely processes,machinery, etc.

In schools, emergency lighting is onlyusually provided in areas not lit bydaylight and those accessible to parents,teachers, pupils and the general publicduring the evenings. These include hallsand drama spaces used for performances.Examples of places where emergencylighting might be considered are escapecorridors, escape stairways and corridorswithout any windows. It should always beprovided in sleeping accommodation. Ifnecessary check escape routes during thehours of darkness to assess whetheremergency lighting is required. In somecases, fluorescent marker lines may be aneffective means of way marking. Thisreduces the level of light necessary to seethe escape route.

It is recommended that for halls,gymnasia and other areas used by thepublic during the hours of darkness theemergency lighting should be of themaintained type which keeps theemergency lighting on at all materialtimes.

On designated escape routes and fireescape stairs the installation can be of thenon-maintained type which will onlyoperate when the normal electric lightingfails, and will operate for not less than 1hour's duration.

Where part of the premises is licensedit will be necessary to seek the advice andguidance of the Local Fire Authority.

The installation should reveal safe


passageways out of the building togetherwith the fire alarm call points, the firefighting equipment, escape signs and anypermanent hazards along the escape routessuch as changes of direction or stairs.

Further detailed guidance is given inthe CIBSE Technical MemorandumTM12: Emergency Lighting 1986 and inthe British Standard Code of Practice forEmergency Lighting, BS 5266: Part 1:1988. The latter is to be replaced byEN 1838, EN 50172 and the EuropeanSigns Directive which is already current.These include details regarding levels ofilluminance, illuminance uniformity andspecific details on escape signs. Thefollowing points (in EN 1838) shouldbe noted.

For escape route lighting and open-area(anti-panic) lighting the emergencylighting shall reach 50% of the requiredilluminance within five seconds and 100%within 60 seconds.

The minimum value for the colourrendering index (Ra) of the light sourceshall be 40.

These criteria will generally be met bystandard, self contained tungsten orfluorescent luminaires.

The primary requirement of anemergency lighting system is that ofsafety. However, there will be considerablevisual benefits from taking this systeminto account when the normal electriclighting is being planned, because it maybe possible to integrate the twoinstallations. Some luminaires are availablewhich can incorporate the emergencylighting as well as the normal lighting:alternatively luminaires can be speciallymodified to do this. The designer shouldbe aware that any luminaire with a CEmark that is specifically modified musthave the original mark removed and theluminaire retested and a new CE markapplied.

The servicing of a building continuesto require more and more equipment,which without a proper integratedapproach, results in visual 'clutter'.Emergency lighting equipment is onepossible cause of this if not properlyconsidered early in the design process.

47

Section 6: Check-list for lighting design

48

The purpose of this publication is to help the architect and the lighting designer tocreate a successfully lit school environment, an environment that is successful in termsof operation and appearance. Since this requires the consideration of a number ofinterlocking elements of building design, it is important that the designer considers theimplications of each element both individually and holistically. Because of thiscomplexity it is stressed that the designer should pay attention to all aspects of theinformation provided in the body of this publication and that the following check-listis used towards the end of the design process to ensure that nothing has beenoverlooked.

The numbers associated with each element of the check-list refer to the sections ofthe publication where further information can be obtained.

6.1 Task/Activity Lighting - 2.1Examine how the space will be used and in particular the tasks and activities that willbe undertaken. For this, consider the following:

Task illuminance (lux or daylight factor) 3.1, 3.2, 4.1, 4.1.1 & 4.2Task illuminance distribution/uniformity 4.1 & 4.2Discomfort glare (sun, sky & electric lighting) 4.1.3, 4.2.1 & Appendix.5Reflected glare (sun, sky & electric lighting) 4.1.3, 4.2.1 & 4.2.3Disability glare (sun, sky & electric lighting) 4.1.3, 4.1.4 & 4.2.1Lamp colour rendering (CIE colour rendering index) - 4.2.5 & Appendix.3Lamp flicker 4.2.2Glare, colour and contrast for visually and hearing impaired pupils 5.11

6.2 Lighting for Visual Amenity - 2.2Determine the appearance of the lighting. Consider the following:

Light pattern 3.1, 3.2, 4.1, 4.1.2 & 4.2.4Subjective lightness 3.1 & 3.2Lamp colour appearance 4.2.5 & Appendix.3Discomfort glare 3.1 & Appendix.5Disability glare 3.1Lamp flicker 4.2.2 & 5.4Exterior/Interior view 4.1.5

6.3 Lighting and Architectural Integration - 2.3Ensure that the lighting equipment, together with its performance, forms anintegrated part of the whole design. Consider the following:

Windows/rooflights 3.1Natural light design/pattern 3.1Luminaire/s 3.2Electric lighting installation 3.2Integration of natural and electric lighting - 4.3Lighting controls Appendix.6

6.4 Lighting and Energy Efficiency - 2.4Check that the lighting installation, both natural and electric, utilises energy effectively.Consider the following:

Natural lighting design (windows/rooflights) 3.1 & 4.1Lamp type/s (efficacy lm/w) 3.2, 4.2.5 & Appendix.3

5 4

Section 6: Check-list for lighting design

Luminaire type/s 3.2, 4.2.5 & Appendix.5Electric lighting controls Appendix.6Integrating electric light with daylight 3.3 & 4.3

6.5 Lighting Maintenance - 2.5Poor maintenance of the lighting installation, both natural and electric, will reducevisual quality as well as waste money and energy. Consider the following:

Degree of environmental cleanliness/dirtinessCleaning and redecoration programme 4.1 & 4.2Lamp life and lamp replacement Appendix.3Disposal of used lamps Appendix.7Luminaire type/s 4.2.5 & Appendix.5

6.6 Lighting Costs - 2.6Lighting constitutes a relatively small part of the capital cost of a school, but none-the-less, it is an important element of design. Consider the following:

Capital cost of the lighting installationRunning costs of lighting equipment

6.7 Exterior and Emergency LightingThese two special topics may not apply to all schools but a positive decision needs tobe made regarding their use -5.13 & 5.14

49

Appendix 1: School Premises Regulations and DfEE ConstructionalStandards for new school buildings.

References:

1. Education (School

Premises) Regulations 1996,

Statutory Instrument 1996

No.360, available from The

Stationery Office.

2. Building Bulletin 87:

Guidelines for Environmental

Design in Schools (Revision of

Design Note 17), 1997, The

Stationery Office,

ISBN 0 11 271013 1.

3. DfEE Constructional

Standards available from

Architects and Building

Branch, DfEE, Caxton House,

6-12 Tothill Street, London,

SW1H 9NF.

Tel: 0171 273 6237

Fax: 0171 273 6762

4. Approved Document L

(Conservation of fuel and

power) in support of the

Building Regulations,

Department of the Environment

and Welsh Office, HMSO

1995, ISBN 0 11 7529338,

£11.

50

The Regulations which apply to bothnew and existing school buildings are theEducation (School Premises) Regulations,1996.(1)

For new school buildings, BuildingBulletin 87(2) is the recommendedenvironmental standard quoted in theDfEE Constructional Standards forSchool Buildings in England.

Schools that are subject to the DfEEConstructional Standards(3) are exemptfrom the procedures of the BuildingRegulations, but the ConstructionalStandards quote the ApprovedDocuments to the Building Regulationsin many cases. For example, in the case offire the Constructional Standards quoteAproved Document B Fire Safety plus theDfEE vaiations given in theConstructional Standards.

The following points from theBuilding Regulations Part L (July 1995),

Conservation of Fuel & Power(4) aresummarised for information.

Part L requires lighting installations tosatisfy two basic criteria:

the light sources and their circuitsshould be of the energy efficient type;and

the lighting installations must becontrolled.

Guidance is given on how to achieveboth these criteria, with alternativemethods for calculation.

To satisfy' the energy efficiency criteriarequires that either 95% of the electriclighting load uses sources such asfluorescent tubes, compact fluorescentlamps or high pressure discharge lamps,or alternatively, the average circuitefficiency should be greater than50 lumens/watt.

Exceptions are permitted, such asdisplay areas or areas where a less efficientsource would be more appropriate.

To satisfy the criteria of controlrequires switches to be placed locally.Arrangements can be made for centralcontrol, provided the central controlpoint is manned or under the control of aresponsible person.

It should be noted that both theCIBSE and DfEE have opted for a highercircuit luminous efficacy of 65 lumens/watt

.ir 4-0

as an average, rather than the 50

lumens/watt as set out in the BuildingRegulations. However the method ofcalculating the value remains the same.

It is recommended that the BuildingRegulations requirements for lightingcontrol are followed as being a sensibleapproach to Energy Conservation, butwith the higher efficacy of65lumens/watt.

Construction Design andManagement Regulations 1994(CDM Regulations)

The CDM regulations apply to most newschool building projects except for minorrefurbishment work. They make it theresponsibility of the designer to informthe client that he is required to appoint aPlanning Supervisor to oversee the Healthand Safety aspects of both the design andthe construction. The designer mustconsider the Health and Safetyimplications of his design and input intothe Health and Safety Plan and theHealth and Safety File. For lightinginstallations, this means that it is theresponsibility of the designer to ensurethat the luminaires can be operated andmaintained in safety. Means for relampingareas such as staircases, gymnasia, halls,external lighting etc, should be allowedfor and where necessary agreed.

56

Appendix 2: Lighting and Health

References:

1. Modulation of light from

fluorescent lamps, Wilkins A.J.

& Clark. C., Lighting Research

and Technology 22 (2)

103-109, 1990, CIBSE.

2. Fluorescent lighting,

headaches and eyestrain,

Wilkins A.J., Nimmo-Smith I.,

Slater kl., & Bedocs L.,

Lighting Research and

Technology 21 (1) 11-18,

1989, CIBSE.

From time to time reports emerge whichsuggest that lighting may be a possiblecause for concern within the workingenvironment. In the past, these haveranged from a cause of headaches and eyestrain to a possible cause of skin cancer.Not surprisingly the lighting professiontakes these reports very seriously andendeavours to investigate the claims toensure that the lighting it recommends isperfectly safe. It is not appropriate todescribe here in detail the results of thevarious studies but to explain the generalunderstanding at present.

One common area of concern is that ofunseen radiation from fluorescent lamps,and in particular ultraviolet radiation:these produce considerably less than thatproduced by the sun. It is considered bythose who have studied this topic that therisk from radiation is extremely smallindeed and is thought unlikely to bea hazard.

Another potential problem is that ofglare and flicker. It has been known forsome time that these conditions can bethe cause of visual discomfort which canimpair vision, reduce visual performanceand in some people cause headaches andeye strain. These temporary afflictions canbe avoided by the use of high frequencyballasts. These topics have been con-sidered elsewhere in this publication andhere the importance of avoiding problemsby good lighting design is stressed.

Some recent research(,2) has shownthat approximately 14% of the populationare susceptible to eyestrain and headachescaused by 50Hz fluorescent lighting andthat this reduces to about 7% with highfrequency fluorescent lighting.

Epilepsy is sometimes triggered by lowfrequency flashes of light by which canoccur with strobe lights, with somecompact fluorescent lamps at ignition, ormore generally with discharge lamps atthe end of their life. Flicker at less than 4flashes per second is unlikely to be aproblem. 50Hz fluorescent lighting hasnot been shown to be a trigger for epilepsy.

There have been in recent times anumber of studies related to 'sickbuilding syndrome'. These studies foundit extremely difficult to determine the

5 7

exact cause of a particular problem, but itis interesting to note that problems rarelyoccurred in buildings with windows whichprovided people with both views out andnatural ventilation. There seems to belittle doubt that windows are aconsiderable benefit to an environment.It is suggested therefore that daylightingand natural ventilation should be apositive feature in school design.

Other studies have shown that peopleprefer lighting which creates a 'light'interior with a non-uniform light pattern.There is currently no evidence that thisform of lighting improves health, but ifpeople prefer it, the feeling of 'well being'which is created can only be beneficial.

The remaining subject to be consideredhere is that of the use of PolychlorinatedBiphenyls (PCBs). Until 1976 thismaterial was used in capacitors as part ofsome fluorescent lamp control circuits.Since that time manufacturers have movedto other materials. In 1986 GovernmentRegulations prohibited the sale of PCBsin small capacitors for lighting equipment,but in existing installations they maycontinue in use assuming they are in aserviceable state. After a period of use,some PCBs may leak from the capacitor,but the amounts invaved are very small.However contact with the body should beavoided and for handling leaky equipmentit is essential to use suitable gloves.Appropriate measures for disposal shouldalso be taken.

In this Appendix an attempt has beenmade to indicate the presentunderstanding of lighting and health as itaffects the school designer. It is felt thatif the guidance presented in thispublication is adhered to, then it is likelythat a well-lit environment will beproduced with risks to health avoided.

51

8E3

Appendix 3: Lamps

This appendix has been included to provide designers with an overview of theperformance of a range of lamp types which could be used in schools. The informationis presented mainly to help the designer make a first selection and it is assumed thatmanufacturers' data will be used for design purposes.

The data on pages 54 and 55 includes information on lamp efficacy, lamp life andcolour performance together with the run-up and re-strike characteristics, anddimming capabilities.

Appendix 3a: Lamp Types

General lighting service (GLS), Reflector (R) and (PAR), tungsten filament lampsAdvantages:Point sources: Excellent colour rendering; Warm colour appearance; Dimmable;Cheap (GLS only, Reflector and PAR lamps are relatively expensive);Instant start;No Control gear required.Disadvantages:Short Life; Low efficacy; Sensitive to voltage variations and vibrations (any structuralborne vibrations which shake the filament will reduce life, consider Rough Service lamps.)

eS Low and Mains Voltage Tungsten Halogen LampsLinear and Capsule TH (K), Reflector TH (M)Advantages:Point source; Excellent colour rendering; Warm colour appearance; Dimmable (Hard fireddimmer required); Instant start; range of wattages, sizes, and beam angles.Disadvantages:Low efficacy; low voltage 12 volt lamps require a transformer; Relatively expensive(compared to GLS); Sensitive to voltage variations and vibrations (any structural bornevibrations which shake the filament will reduce life, consider Rough Service Lamps).

EE

Low Pressure Mercury Discharge Tubular Fluorescent Lamps (MCF)Advantages:Linear lamp, with some exceptions (circular, U shape not widely used old technology);High Efficacy; Various colour appearances, Cheap; Long life; 112 - Halophosphate oldtechnology 38mm tube, less efficient than - T8 26mm lamps Triphosphor, Generallybetter colour rendering than T12, new generation have low mercury content and lowoutput depreciation. 15 - Triphosphor smaller lamp diameter 16mm tube, highestefficacy. All run off High Frequency Control gear, 112 & 18 will also run off Standard andlow loss wire wound ballasts. Dimmable circuits are available for most types offluorescent lamps.Disadvantages:Diffuse source; standard lengths; Control gear required; T5 only works on HF gear whichis expensive.

=[:Low Power Compact Fluorescent Lamps (SL, PL, 2D, 2L)Advantages:Smaller size than linear fluorescent; Some lamps dimmable; High efficacy;Long life; Relatively Cheap; some sizes can be used as direct tungstenlamp replacements (complete with control gear). High frequency gearavailable for higher wattage lamps (greater than 2x13w).Disadvantages:Diffuse source; Requires control gear; most circuits run at low powerfactor; tube wall very bright, can cause glare.

52

Lamp illustrations reproduced from CIBSE Code for interior lighting (1994) with the permission of theChartered Institution of Building Services Engineers, 222 Balham High Road, London, SW12 9BS

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Appendix 3: Lamps

Appendix 3b: Lamp Types

Low Pressure Sodium Lamp (SOX)

Advantages:Very High efficacy; long Life; relatively cheap; various wattages.

Disadvantages:Mono-chromatic (yellow) light; no colour rendering; requires control gear. Run-up timerequired to reach full output.

2(ff

High Pressure Sodium (SONDL)

Advantages:High efficacy; Long life except 'white SON.

Disadvantages:Effect of light source can be oppressive when used in an interior, except 'white" SON;poor to average colour rendering except 'white' SON which is good; colour appearance iswarm (golden white); Requires control gear; requires run-up time.

High Pressure Mercury Vapour (MBF)

Advantages:Long life; various wattages; De luxe versions average to good colour rendering; relativelycheap.

Disadvantages:Generally poor to average colour rendering; poor efficacy; requires control gear; requiresrun-up time. Blue-green white light.

4

.IMIININ':'

it7-702

High Pressure Metal Halide Lamps (MBI, MBIF)

Advantages:High efficacy; good colour rendering; warmfintermediate/cold colourappearance versions available; average to long life depending on wattage.Ceramic arc versions - good colour stability, longer life.

Disadvantages:Some lamps change colour through life; high UV output-source needs glasscover; failure unpredictable; No British Standard. Requires control gear;requires run-up time. Ceramic arc versions - more expensive.

Induction Lamp

Advantages:Very long life (except reflector lamp which is long life); low pressure lamp; good colourrendering; no flicker; virtually maintenance free.

Disadvantages:Limited range; high electromagnetic radiation generated, requiring careful use; smalllumen packages; diffuse source.

BEST COPY AVAILABLE

Lamp illustrations reproduced from CIBSE Code for interior lighting (1994) with the permission of theChartered Institution of Building Services Engineers, 222 Balham High Road, London, SW12 9BS

4 53

Appendix 3: Lamps

Appendix 3c: Lamp data

Colour Rendering Efficacy Typical lamp life Typical range Control gear Lamp start-up Lamp re-strike

Lamp type group/Colour (approximate) (hours) of lamp power required time time.

Temperature, K Lumens/Lamp Watt rating (Approx) (see Note 4)

Tungsten (see Note 3) (see Note 2) (wattage)

Mains (230V)GLS and reflector 1A/2700K 8-12 1000 15-1000 No Instant Instant

PAR 1A/2700K 10-12 2000 80-500 No Instant Instant

Tungsten halogen 1A/2900K 10-18 2000 50-100 No Instant Instant

Linear tungstenhalogen 1A/2900K 14-22 2000 60-2000 No Instant Instant

Low voltage (12V)tungsten halogen 1A/3000K 12-25 3000-5000 5-100 Transformer Instant Instant

Fluorescent

T12(Halophosphate) 2/3000-5000K 60-80 7500 20-125 Yes 1-3 secs 1-3 secs

T8 (Triphosphor) 1A,18/3000-6000K 60-95 7500-15,000 18-70 Yes 1-3 secs 1-3 secs

15 1B/3000-4000K 95-110 10,000-15,000 14-50 Yes 1-3 secs 1-3 secs

Circular 2/3000-5000K 30-50 7500 22-60 Yes 1-3 secs 1-2 secs

Compact 1B/3000-6000K 43-83 7,000-10,000 5-55 Yes 1-3 secs 1-3 secs

Low pressureSodium (SOX) None 100-190 12,000-16,000 18-180 Yes 8-12 mins Prompt <55w

10 mins >90w

High pressureSodium (SON),

Standard 4/2000 65-140 16,000-20,000 50-1000 Yes 1.5-6 mins >1 min

De luxe 2/2200 75-90 12,000-16,000 150-400 Yes 5-6 mins >1 minWhite 1B/2500 35-50 5,000-10,000 35-100 Yes 5-6 mins >30 secs

MercuryVapour (MBF)

Standard 3/4000 40-60 24,000-29,000 50-1000 Yes 2-5 mins 4-7 minsDe Luxe 2/3400 40-60 24,000-29,000 50-400 Yes 2-5 mins 4-7 mins

Metal halide(MBI)

Single ended 18,2/3000-4200 60-68 6000 70-150 Yes 3-6 mins 6-10 minsDouble ended 18,2/3000-4200 68-75 6000 70-250 Yes 3-6 mins 6-10 minsTubular/elliptical 1A,2/4000-6000 70-80 6000-15000 70-1000 Yes 3-6 mins 6-20 minsCeramic arc tube 1B/3000 70-75 6000-8000 35-150 Yes 3-6 mins 6-10 mins

Induction

Standard 18/3000-4000 70 60,000 55-85 Yes Prompt Prompt

Reflector 1B/3000 47 10,000 23 Built in Prompt Prompt

5BEST COPY AVAILABLE 60

Notes to Appendix 3: Lamps

Note 1: The tabular data provide anindication of lamp performance: for exactdata, information from manufacturersshould be consulted.

Note 2: The power consumption of thecontrol gear associated with dischargelamps should be included in estimatingthe efficacy of the installation: values varyand should be obtained from themanufacturer.

Note 3: See tables on the right forcolour rendering groups and correlatedcolour temperature classes as defined byCIE.

Note 4: The re-strike time after aninterruption to the electrical supply.'Prompt' re-strike is not instantaneousbut barely noticeable. Instant re-strike isavailable for all double ended highintensity discharge lamps using specialhigh voltage ignitors, but they are tooexpensive for general use and do notaffect the lamp start-up time.

Appendix 3: Lamps

Colour renderinggroups

CIE general colourrendering index (Ra)

Typical application

1A Ra 90 Wherever accurate colour matching isrequired,eg, colour printing inspection

1B 80 5 Ra < 90 Wherever accurate colour judgements arenecessary and/or good colour rendering isrequired for reasons of appearance, eg,shops and other commercial premises.

2 60 5 Ra< 80 Wherever moderate colour rendering isrequired.

3 40 5 Ra< 60 Wherever colour rendering is of littlesignificance but marked distortion of colouris unacceptable.

4 20 5 Ra< 40 Wherever colour rendering is of noimportance at all and marked distortion ofcolour is acceptable.

Correlated Colour Temperature (CCT) CCT Class

CCT 5 3300 K Warm

3300 K < CCT 5 5300K Intermediate*

5300 K < CCT Cold

* This class covers a large range of correlated colour temperatures. Experience in theUK suggests that light sources with correlated colour, temperatures approaching the5300 K end of the range will usually be considered to have a 'cool colour appearance.

Appendix 4: Control gear

All discharge lamps require control gearto limit the current taken by the lamp itcontrols. There are various types ofcontrol gear which effect the overallperformance of a lamp.

Control gear for Fluorescentlamps

Standard control gear consists of a basicunit with relatively high losses andharmonic components. Unless specifiedotherwise most luminaires will besupplied with this gear.

Low loss gear is slightly more expensivebut generally the losses are half those ofstandard gear. The physical size allows itto be installed in most luminaires. For

BEST COPY AVAILABLE

energy efficiency this is the minimumstandard which should be adopted.

Super low loss gear is more expensivethan low loss gear with roughly half thelosses but the physical size is largermaking it difficult to use in mostluminaires.

High frequency gear is electronic gear. Itis lighter and has the lowest electricallosses of all the conventional types of gear.It is much more expensive thanconventional (wire wound) gear. It can besupplied in dimming form (moreexpensive still).

There is no simple payback advantagefor this type of gear, at present. The life ofthe gear (not yet proven) is thought to be

55

Appendix 4: Control gear

less than conventional gear and it is moresusceptible to high temperatures(50-60°C).

Other advantages apart from low powerlosses are: it is flicker free; it reduces risksof epileptic fits; and it has a 'soft' start(increases lamp life).There are two types of high frequencycircuits, analogue and digital. Digital ismore expensive but provides smootherdimming whilst analogue circuits providestep dimming. The choice will depend onthe degree of control required.

Electronic starters. There are a numberof canister type electronic startersavailable which provide a 'soft' start.These are slightly more expensive than astandard glow switch starter but whenthese electronic starters are combinedwith low loss gear many of the features ofthe high frequency circuit are providedbut at a much lower capital cost.

Control gear for high pressuredischarge lamps. Most lamps requiretheir own dedicated control gear forefficient operation. However, there aresome high pressure sodium lamps whichwill operate on mercury vapour lamp

Appendix 5: Luminaires

56

This appendix provides designers with anoverview of the performance of a range ofluminaire types so that simple comparisonscan be made. The information is intendedto help the designer make a first selectionand that manufacturers' data will be usedfor design purposes.

The first data sheet is concerned withluminaires used in a regular array.Information is included on suitable lamp

62

control gear. These are special lampsdesigned to be used as replacementsources for mercury lamps.

Metal Halide lamps. Most metal halidelamps require an ignitor which produces a5kV pulse to start the lamp. It is essentialto keep the ignitor close to the lamp,unless special high voltage cable is usedwhen the ignitor can be remotelymounted. At the end of their life metalhalide lamps can cycle and eventually mayrectify. These conditions can be annoyingand dangerous. It is advisable to specifythe use of timed ignitors which will shutthe circuit down before any damage canbe done.

Mercury Vapour lamps. Power switchesare available for some circuits whichallows the lamp to run at reduced outputand reduced power. This could be usefulfor areas where lighting is required duringunoccupied times, or for security lightingwhen the lamps could be run all night atreduced consumption.

Sodium lamps. A similar power switch isavailable for some high pressure sodiumlamp circuits.

types, light output and distribution,luminaire mounting and spacing,utilisation factors and glare indices.The likely distribution of light within aspace is also included.

The second sheet is concerned withluminaires used individually: in additionto lamp types, some general informationis provided and a variety of data isavailable from manufacturers.

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APPENDIX 5 (CONTINUED): LUMINAIRES USED INDIVIDUALLY

TASK/LOCAL LUMINAIRESOften fitted with an integral dimmer and transformer. Someluminaires which are generally used in regular arrays (pages 5758) can also be used individually for localised lighting.

GLS R TH(K) TH(M) MCF SL PL 20 2L

SPOT FLOOD

I ACCENT & DISPLAY LUMINAIRES (SPOTLIGHTS &FLOODLIGHTS)Generally wall, ceiling or track-mounted in either mains or low-voltage versions. Total beam widths are as follows: pencilk10°);narrow (10-25°); medium (25401; wide (>40°).

GLS PAR TH(K) TH(M) SL PL 2D 2L MBI

V

FREE- STAMOI N WALL

UPLIGHT LUMINAIRESAvailable in free-standing and wall-mounted versions and a varietyof light distributions. Occasionally used in regular arrays.

GLS TH(K) MCF SL PL 20 2L MBI MBIF SONDL

WALL-WASHING LUMINAIRESUsed to emphasise vertical surfaces.

GLS TH(K) MCF PL 2L MBI

DOWNLIGHT LUMINAIRESAvailable in recessed or surface-mounted versions. Often used inregular arrays.

GLS PAR R TH(K) TH(M) SL PL 2D 2LMBF MBI MBIF SONDL

65BEST COPY AVALABLE 59

Appendix 6: Lighting Controls

60

The lighting controls of an installation,ie, the switches, dimmers, etc, are animportant part of a lighting design andneed careful attention if the installation isto be convenient to operate and energyefficient. If the light switches are placednear the entry/exit point from generalcirculation, this is convenient, but theswitches need to operate the luminairesrelative to the distribution of daylight, ie,it should be possible to switch off theluminaires which are near the window,whilst keeping the lights on at the back ofthe room. In the first instance theswitching of the lighting installationshould be planned both to accommodatethe convenience of the users and to allowthe electric lighting to be switched tocomplement the daylight distribution.The arrangement of the switches on theswitch plate also needs to be considered ifthe users are to operate the lighting withthe minimum of inconvenience.

In many schools, the electric lighting isusually on longer than is necessary. Oftenthe lighting is switched on first thing inthe morning, perhaps by the cleaners orthe first person to arrive, and because it isthen overlooked it is left on all day untilthe last person leaves in the evening. Thisoccurs, even though for a considerablepart of the day, natural light would besufficient to light the space and is a wasteof energy and money. There are a widerange of automatic lighting controlsystems available, some of which arecomplex, and therefore too expensive forthe typical school situation.

Time-switch controls

One system which is relatively inexpensiveand which is likely to produce considerableenergy savings, is a time-operated switchwhich will switch off all or some of theluminaires at a time in the day when it islikely that there will be sufficient daylightpresent. It must however be possible toover-ride the time-switch at any time thatthe users feel it necessary to switch on all,or some of the lights. The automaticswitch-off time will depend on theparticular daylight design, but it would beconvenient if it could occur at a natural

66

break in the day, eg, the mid-morning orlunch-time break. If after the break thereis sufficient daylight, then the electriclighting will remain off until the daylightlevel falls below an acceptable minimum.For this type of control it is necessary tohave special devices in individualluminaires, or groups of luminaires, toallow them to be switched off by amomentary break in the electricity supplywhich is activated by the time-switch.There should also be switches which theuser can operate to switch on theluminaires at any time that they arerequired.

Photocell controls

The next level of automatic lightingcontrol is to use light responding switchesor photocell controlled switches. Thesewill switch off luminaires as the daylightreaches a required level. The lighting canthen be switched on again by the user asrequired. The designer should assess theperformance and cost effectiveness ofthese automatic control systems.

Occupancy Controls

Another type of lighting control is theoccupancy sensor controlled switch. Thisis a device that responds to the occupancyof a room. It can be used to switch lightson as people enter the space or switchthem off when a room is not being used.These types of controllers are appropriatein intermittently occupied rooms. Theyhave been used to good effect in toiletsand changing rooms, and in assemblyhalls and sports halls where energy savingsof 25-30% and payback periods of 3 yearsor less are possible (Fig 40).

It should be noted that frequentswitching of light sources can have adetrimental effect on the lamp life. Usinghigh frequency gear or electronic softstarts for fluorescent circuits can help toprolong lamp life.

Dimmers

Dimmers, or lighting regulators, can beused to adjust light levels between full

light output and off or in the case ofsome fluorescent lamp circuits toapproximately 10 or 20% of fill lightoutput. These controllers are useful inrooms where visual aids are to be used,eg, overhead, film and slide projectors.Here the lighting can be dimmed toreduce the lighting level so that theoverhead, film or slides can be seencomfortably but with sufficient light toenable notes to be taken. Other situationswhich probably require dimming circuitsare drama studios and general purposehalls if these are to be used for drama orother events. If a dimming circuit is to beincluded, it is important to use lampswhich can be dimmed satisfactorily. Theseinclude incandescent, tungsten halogenand some fluorescent lamps includingcold cathode types. For schools it wouldbe inappropriate to use high pressuredischarge lamps in places where dimmingis required.

Drama studios and halls which are tobe used for theatrical presentations alsorequire stage lighting control equipment(see section 5.8). Stage lighting is of aspecialist nature and the choice willdepend on the sophistication requiredand it is suggested that the manufacturersare consulted.

In-Luminaire Controls

Luminaires are available which containelements of automatic control which canbe beneficial to the end user. The systemsare relatively simple to use, are cheaper toinstall (as no switch is required at the door);.,ut the luminaires are more expensive.

These controls vary from a simpleon/off device, presence or absencedetectors, through to more sophisticatedunits which can be set to provide amaintained illuminance, daylight linked toallow for daylight by dimming, up toindividual control by means of a handheld override unit.

This method of control is probablyonly going to be worthwhile wheredaylight linking and the maintenance of aset illuminance are going to be adopted asa means of reducing the operating costsof the building.

APPENDIX 6: Lighting Controls

It is unlikely that the moresophisticated type of control will producea short payback period, but developmentsin electronics are such that these devicesshould be kept under close scrutiny.

Individual 'clip-on' light sensors can beused to help maintain a set illuminance.These can simply be attached to anyluminaire with an analogue dimmableballast.

6761

Appendix 7: Disposal of used lamps

Fluorescent tubes, compact fluorescentlamps, high pressure mercury lamps,metal halide lamps and high pressuresodium lamps all contain mercury. Theamount of mercury varies between about5mg and 35mg depending on themanufacturer and the age of the lamp.

Fluorescenttubes

CompactFluorescent

lamps

High

Pressuremercury

MetalHalide

HighPressureSodium

Lowpressuresodium

Mercurymilligrammesper lamp(mg)

20 - 35 20 - 35 20 30 - 45 10 - 20 0

Sodiummilligrammesper lamp(mg)

0 0 0 3 5 400

Average weightof lamp (g)

200 200 100 150 300 300

62

Some of the mercury is absorbed into theglass, some is present in the phosphorlayer and some is present as free mercury.Many older lamps also contain cadmiumwhich is a known carcinogen. This needsto be considered during disposal. Lampscurrently manufactured in Europe do notcontain any cadmium.

Fluorescent tubes also contain rareearth metals such as antimony. Howeverthe main concern is mercury. It fulfilsessential physical functions within the gasdischarge and there is no substitute. TheEC permissible limit for mercury is onlyone part per billion in drinking water.This gives an indication of its toxicity. Itis worth remembering that mercurycontained in fluorescent lamps is only asmall part of the mercury released to dieenvironment. The UK Lighting IndustryFederation states that only 0.3% of themercury entering the environment comesfrom lamps. Nevertheless the totalamount of mercury contained in theworld's annual production of lamps hasbeen estimated at 75 tonnes.

The CIBSE Interior lighting guideappendix 5.11 Environmental aspects oflighting gives an analysis of the totalamount of mercury released to theenvironment both by the production ofthe electricity used by the lamp and bythe disposal of the waste lamp at the endof its life, for the different types of lamp.

This shows that compact fluorescentlamps have the most mercury in the wastelamp per KWh of electricity produced.However, due to their inefficient use ofelectricity, ordinary filament lamps lead toa greater release of mercury to theenvironment, than any other type oflamp, although the waste lamp does notcontain any mercury.

It is best from an environmental pointof view to arrange for used lamps to berecycled by a specialist company. Sweden,Austria and America have been recyclingused lamps to recover the mercury formany years and this facility is nowavailable in the UK. Mercury presents along term threat in the environment.Free mercury may be safely absorbed atfirst but in time can react to formmercury metal compounds which can bemore dangerous.

The charge for recycling is currentlybetween £0.25 £0.50 per tube. Theprice reduces with increasing quantities oflamps, therefore it may be desirable tostore used lamps until there are asufficient number to benefit from areduced rate. Some relamping contractorswill arrange to recycle lamps as part oftheir contract. Alternatively schools canconsult their waste disposal companyabout the method of disposal used andwhat facilities are available for recyclinglamps. Some of the big waste disposalcompanies are now linked to thespecialists who recycle lamps. Sites thatrecycle lamps containing mercury need alicense to do so.

There are safety implications of storingused lamps on site and a school doing thishas a duty of care to do it safely. If lampsare stored for more than one school alicense to do this will be required fromthe local waste regulation authority.

Questions on disposal are usuallydirected to the Local Office of theEnvironment Agency which hasresponsibility for implementing the 1990Environmental Protection Act and the1996 Special Waste Regulations. Lampsfrom schools are not classified as SpecialWaste under the 1990 EnvironmentalProtection Act. Waste from schools isclassified as household waste and under

68

the 1996 Special Waste Regulationshousehold waste, as defined by the EPA,cannot be Special Waste, unless it isasbestos or comes from a laboratory. Inany event lamps containing mercurywould not be classed as Special Wasteunless they contained over 3% by weightof mercury, or they contained sodium aswell as mercury. However, low pressuresodium lamps which have not beenbroken would be classed as SpecialWaste(unless they are present inhousehold waste) due to the risk of thesodium igniting. The manufacturersinstructions with each lamp contain therecommended safe method of storage anddisposal. They can be broken inaccordance with the manufacturersguidelines and doused with water to reactwith the sodium. The liquid can then beput down the drain and the glassfragments treated as ordinary waste.

The breaking of fluorescent tubes is ahazardous operation. However, smallquantities of unbroken fluorescent tubescan be put into the normal domesticrefuse. Where lamps are replaced in largequantities the used lamps must be treatedas difficult waste and taken to a sitelicensed to handle them. Although it ispermitted to dispose of used lamps tonormal land fill sites they are becomingincreasingly wary of taking wastecontaining mercury, and disposal via aspecialist recycling company is preferable.

Lamp Breakage

When lamps have been removed fromservice the principal hazard is brokenglass. Placing them in the packagingprovided with the new lamps is one wayof protecting them from accidentalmechanical breakage or scratching, whichcould lead to glass fracture and possiblyflying fragments. Special storage bins areavailable from lamp recycling companies.Where recycling is not possible and it isnecessary to break lamps to reduce bulk,good housekeeping practice should befollowed, ie, protective clothingincluding gloves should be worn, andpreferably the operation should be in awell ventilated area or outdoors.

Appendix 7: Disposal of used lamps

Many lamps are filled to pressuresabove or below atmospheric pressure andtherefore care must be exercised infracturing the lamp envelope. Wheneverglass is broken it is a requirement of theProtection of the Eyes Regulations 1974that eye protection must be worn.

Only the outer envelopes of highpressure discharge lamps should bebroken. The inner arc tubes are strongand should be left intact as a container ofthe lamp constituents, eg, small quantitiesof mercury.

If there are large numbers of lamps tobe broken, machines are available whichbreak the glass while at the same timespraying the debris with water to preventpowder flying and to react any sodium ifthis type of lamp is being crushed. Theadvice of the local water supply companyshould be sought regarding the safedisposal of this water (StatutoryInstrument SI 1156 must be observed).The purpose of this appendix is to show Reference:

Statutory Instrument, 1989No.1156, Water, England andWales, The Trade Effluents(Prescribed Processes andSubstances) Regulations 1989

63

Appendix 8: Examples of lighting design strategies

64

the development of lighting designdecisions based on the criteria describedin the body of the document. It does notgive completed designs but shows theconsiderations and processes involved bymeans of illustrative examples. Thesolutions are not meant to be 'ideal', andshould not be used for an actual projectwithout checking that they are satisfactoryfor the particular situation. Everysituation is different and the designer hasto respond to the actual circumstancesincluding the user requirements and tothe interpretation of the constraints. Theexamples are not related specifically toeither primary or secondary schools butare considered to be appropriate for eitherwith some modifications to suit theparticular case.

The first example (Appendix 8.1)explores the interaction between thebuilding and its site. It examines thevarious factors which can influence theactual position of the building on the siteand also the exact location of classroomsand other areas.

The second example (Appendix 8.2)considers a typical basic classroom unit of2.7m height (floor to ceiling), and it ispresumed that there is only one externalwall. The basic daylighting performanceis evaluated and it is then extended toconsider how this might change by theaddition of a rooflight or clerestorywindow at the back of the room. Theelectric lighting is then explored, for bothfunction and appearance, in terms ofsupplementing the daylight whennecessary and at night-time.

The third example (Appendix 8.3)considers a fairly typical two-storey atriumspace. A number of glazing arrangementsare investigated with regard to theirdaylighting performance both within theatrium and in adjoining rooms, and toother factors including visual contact withthe outside. Three electric lightingschemes are examined and, as with thedaylighting, maintenance of thecomponent items is considered.

It is emphasised that these examples donot provide solutions to be followed inpractice; they are illustrative examples todemonstrate strategic and other more

I14

-

detailed considerations concerned withlighting design for schools.

APPENDIX 8.1 SITE ANALYSISThe orientation and position of a buildingon a site can affect the quantity andquality of light entering spaces, inaddition to taking advantage of anypleasant view. The following diagramsshow some of the influences on thispositioning and indicate advantages anddisadvantages in relation to a notionalsite. This bulletin is not concerned withthe additional problems of access andnoise intrusion, although these twofactors also affect siting.

70

ORIENTATION

winter solsticery,

S

equinox

," 04"

- summer solstice

Diagram showing sun's path for summer & winter solstices andthe equinoxes for approximately a latitude of 52°N (London)

SOLAR GAIN

OVERSHADOWING

14,

Appendix 8.1: Site analysis

0.97

Diagram showing daylight orientation factors.The luminance of the southern sky is greater than that of thenorthern sky (see section 4.1.1)

Heat generating activity should not be planned on that side of a buildingwhere solar heat gain is likely to be a problem unless protective measuresare employed (see section 4.1.4)

Tall buildings and dense trees can screen fromlow angle sun

vIEW

LIGHT TRESPASS

oto.

Tall buildings and dense trees can overshadow, reducingthe amount and penetration of daylight

Views provide considerable benefit(see section 4.1.5)

Night time righting of playing areas can cause annoyance toneighbours. 'Spill light' and glare from floodlights should beminimised (See section 5.13).

BEST COPY AV 6 5

DIAGRAM 'A' BUILDING ON NORTH OF SITE

NORTH FACINGCLASSROOMS

SOUTH FACINGCLASSROOMS

ORIENTATION low sky luminance high sky luminance

SOLAR GAIN none risk of gain in summer

OVERSHADOWING none none

VIEW very pleasant less pleasant

LIGHT TRESPASS a possibility a possibility

\\\

DIAGRAM 'C' BUILDING ON WEST OF SITE

EAST FACINGCLASSROOMS

WEST FACINGCLASSROOMS

ORIENTATION medium sky luminance medium sky luminance

SOLAR GAIN lithe risk little risk


VIEW pleasant less pleasant

LIGHT TRESPASS low possibility due to

screening by school

low possibility due to

screening by school

BESTCOPY AVAILABLE

Appendix 8: Site analysis

This figure represents a notional site with commonlyoccurring features:neighbouring tall building and trees;pleasant view;busy road and view to industrial estate;neighbouring housing.

For the purpose of the example, the north point hasbeen placed to the top of the site.

The plan is not to scale.

The following diagrams indicate some advantages anddisadvantages of placing a school in various positionson the site: for clarity the plan is over-simplified.

It will be seen that the best result must be acompromise after the various components have beenconsidered.

DIAGRAM 'B' BUILDING ON EAST OF SITE

EAST FACINGCLASSROOMS

WEST FACINGCLASSROOMS

ORIENTATION medium sky luminance medium sky luminance

SOLAR GAIN little risk lithe risk

OVERSHADOWING In early morning from

tall buildings

none

VIEW less pleasant pleasant

LIGHT TRESPASS a probability a probability

DIAGRAM 'D' BUILDING ON SOUTH OF SITE

NORTH FACINGCLASSROOMS

SOUTH FACINGCLASSROOMS

ORIENTATION low sky luminance high sky luminance

SOLAR GAIN none risk of gain in summer


VIEW very pleasant least pleasant

LIGHT TRESPASS a possibility a possibility

72 66

Appendix 8.2: A typical classroom

APPENDIX 8.2: A TYPICAL CLASSROOMThis worked example considers a typical classroom (8 x 6.5m) with aminimum height of 2.7m and an external wall 6.5 x 2.7m(Scheme A). The room is expected to be used for general teachingactivities including reading, writing and craftwork. The classroommay have a formal teaching position together with pin-up boards todisplay student work. Alternatively, it may be used informally. Theaim is for the classroom to be mainly daylit for most of the time andto have electric lighting to complement the natural light whennecessary. At night-time the electric lighting will provide good seeingconditions for all but the most difficult tasks when supplementarytask lighting can be employed. The following schematic explorationshows the development of possible lighting solutions together withthe expected performance.

INITIAL DAYLIGHTING STRATEGYConsider a typical window (6 x 2m), SCHEME A, and its daylighting performance :

Section A

J

/

1

SCHEME A Figure 1

Average Daylight Factor N = TWO whereA(1- R2)

T = glass transmittance, including maintenance factor (0.8 x 0.9 = 0.72)W = glass area (12m2)0 = window sky acceptance angle (65°)A = total room surface area (182.3m2)R = area-weighted reflectance (0.45)Values in brackets are those used for initial calculation.

= 3.9% Minimum DF = 1%

If double glazed (ie, T = 0.65 x 0.9 = 0.59) thenDF = 3.1% Minimum DF = 0.8% (Figure 1)

If most of external wall is glazed (ie, W = 16m2), SCHEME A", then

10 5 I

1

1

21 1

1

SCHEME A* Figure 2

= 5.2% (single glazing) Minimum DF = 1.25%Dr = 4.2% (double glazed) Minimum DF = 1% (Figure 2)

(Minimum Daylight Factor values found from point calculation method usingthe standard CIE overcast sky).It can be seen that, even with a fully glazed wall, a DF of 5% (the minimum designobjective for a 'well' daylit room) can only be achieved with single glazing which willencounter thermal problems.

DAYLIGHT ILLUMINANCEThe following table indicates the orientation-weighted Daylight Factors (see Table 4,page 17) required to provide various levels of daylight illuminance.Note: orientation-weighted Daylight Factor = DF (CIE overcast sky) x orientation factor.

UnobstructedIlluminance

% of year forwhich illuminance

Orientation weighted daylight factors toachieve given lighting levels

lux is exceeded in UK 100 lux 200 lux 300 lux 500 lux

5,000 84 2% 4% 6% 10%

10,000 68 1% 2% 3% 5%

15,000 p 0.67% 1.34% 2% 3.33%

ANALYSISThe typical window investigated (12m2) will not provide sufficient daylightfor the whole year. For approximately half the time electric lighting willbe required at least at the back of the room.There are two possible solutions: a) increase daylighting by the additionof a rooflight or clerestory if possible. and b) provide electric lighting tosupplement daylight when required.Two extended daylighting solutions have been investigated (Schemes B and C) andthe likely perfOrmances are shown in the illustrations (Figures 3 and 4).

67

BEST COPY MAI LE

ii

SCHEME B

II

1

10i 51 21I

i/

Figure 3

SCHEME C Figure 4

Ceiling reflectance = 0.7

2m

1-

2.7m

Scheme An"( full t glazing)

6.5m Floor reflectance = 0.2

-oo Wall reflectance = 0.5

Typical classroom SCHEME A(glazed above 0.6m high cill)

Rooflight improvesdaylight distributionto back of classroom

SCHEME B

High level clerestorywindow improvesdaylight distribution toback of classroom

7468

SCHEME C

al a2

al a2 a3

a

IRON*

Typical classroom SCHEME A

a

1000111

SCHEME B

75, ,

69

Appendix 8.2: A typical classroom

ELECTRIC LIGH11NGAssume a basic requirement for a Task Illuminance of 300Ix with a horizontal plane uniformity ofnot less than 0.8 and a Limiting Glare Index of 19. Suggest using a regular array of 'Semi-Direct'distribution luminaires equipped with a single 1.5m 58w tri-phosphor lamp (Average Lamp LightOutput = 5100Im) (Appendix 3).

Room Index = 1.8 (A measure of the proportions of a room. See CIBSE Code for Interior LightingSection 4.5.3.2), Typical Utilisation Factor = 0.6 (Appendix 5), Maintenance Factor at end ofone year = 0.86

Illuminance x AreaNo. of luminaires = 6 luminaires

Utilisation Factor x Maintenance Factor x Lamp Light Output

With a 2x3 array, the maximum spacing = 6.5/2 = 3.25Maximum Spacing to Mounting Height ratio = 3.25/1.95 = 1.7 (acceptable)Glare Index = not greater than 19 (Appendix 5)

Luminaire layout as shown in illustration individually switched in rows al, a2 and a3 parallel to thewindow. In addition to the regular array, a line of luminaires should be included to illuminate theback wall (Scheme A).

Variations on the basic proposal are shown for the schemes which utilise rooflights andclerestories (Schemes B and C). NOTE: FOR ACTUAL DESIGNS USE MANUFACTURERS'PHOTOMETRIC DATA

ENERGY EFFICIENCYTo ensure maximum energy efficiency without compromising the quality or visual effectiveness ofthe installation, consider the following:

O To optimise use of daylight install photocells or time-switches to turn electric lighting off whennot required (possibly during mid-morning break). Also provide manual over-ride in classroom.

O Install lighting controls (switches) in a logical way to ensure only the luminaires required willbe switched on.

O Consider using high frequency control gear to improve visual comfort and energy efficiency.

O Implement regular lighting maintenance programmes.

CONCLUSIONSThe basic design with side windows only (window area 12m2) is likely to provide-adequatenatural light conditions for approximately hatf the year depending on window orientation(Scheme A).

The windows will provide acceptable view out but window blinds may be necessary to obscuredirect sunlight depending on the window orientation and external obstructions.

When the natural light is insufficient this can be supplemented by luminaires at theback of the room.

The regular array of luminaires will provide good working conditions over the whole horizontalplane with an acceptable comfort level. The luminaires which provide wall lighting at the back ofthe room will accent the wall display and enhance the visual appeal of the room (Scheme A).

The two proposals with the addition of either a rooflight or clerestory window provide a higherlevel of daylight and hence a potential reduction in the use of electric lighting. They will alsoproduce a better visual environment (Schemes B and C).

The accent lighting aims to provide an additional visual focus. However, it is important that thisequipment integrates with the design of the classroom. This also applies to the regular array ofluminaires for the general lighting.

70

Appendix 8.3: An atrium

APPENDIX 8.3: AN ATRIUM

r'possible clerestory 4,1

first floor teaching room

Access galleryrto upper rooms

4-- open or glazed

zone of possible roof glazing

'555,'55

14 possible clerestory

open access gallery 4 glazingfirst floor teaching room

ground floor teaching room

71

4 glazing

ATRIUM

ground floor teaching room

DIAGRAM SHOWING POSSIBLE SECTION THROUGH TYPICAL 2-STOREY SCHOOL ATRIUM

The space could to be used for school assembly, dining, general socialising and private or groupstudy, in addition to circulation and display. It may be landscaped, using suitable plants, and canform a focal centre. AtTia will be predominantly lit by daylight when available and they cancontribute to the enhancement of the visual environment of surrounding areas, by providing achange of view, and by increasing daylight availability to the rear of teaching rooms which mightotherwise be lit from one side only on their window wall.

There are some general factors to be taken into account when considering atrium design from thelighting point of view. For example the level of light should neither be so high that adjoiningspaces appear dim by comparison nor so low thit the atrium itself appears under-lit when viewedfrom these spaces. In order to achieve a satisfactory distribution of light particularly in the lowerareas of the space, it is important that the majority of surfaces, in particular those on the verticalplane, have a higher reflectance value. This should also include the floor and furniture. Theorientation of the atrium glazing will be influential in relation to sun and sky glare, and solar gain.Clear glass is recommended in order to give a view_out and to cut out sunlight diffusion whichoccurs with translucent materials. If solar control glass is used, consideration should be given tothe possibility of colour distortion and the creation of an 'under-lit' effect. Sky luminance isanother factor (see section 4.1.1).

Spaces of this type are often two storeys or more in height and provision for cleaning andmaintenance of the glazing and luminaires is necessary.

The additional problems of acoustic and thermal environments are not specifically dealt with here,although these factors will have to be considered in atrium design.

The following diagrams show some of the main factors to be considered.

,

IJ

72

/no"

ss

//

/

SKY GLARE

In top glazing, sky glare is likely to be more ofa problem than in side glazing, because theluminance of the upper part of an overcast skyis greater than that of the lower. This can beameliorated by ensuring that areas surroundingglazing are light in colour, and by the use ofadjustable louvres or blinds.

SUNLIGHT GLARE AND SOLAR GAIN

Sun glare and solar gain can be a problemwhich can be controlled by the use ofadjustable louvres or blinds, and by appropriateorientation. The admission of some sunlighthowever will enliven the visual scene. Insummer, solar gain will cause overheatingunless controlled, whereas in winter it cancontribute to the thermal environment.

SUPPLEMENTATION of DAYLIGHT toADJOINING SPACES

The atrium can be used to make a contributionto the lighting of the part of an adjoining roomfurthest away from the window wall, bysupplementing the daylight.

VISUAL CONTACT WITH EXTERIOR

Visual contact with the exterior through theglazing is desirable and diffusing glass is notrecommended.

DAYLIGHTING

The advantages and disadvantages of the following glazing arrangements are examined with respect to the factors discussedearlier. For the two basic forms an atrium of 15m x 10m in plan, with a height of 7.5m to the top of the wall and 10m to theridge is considered. Double glazing is assumed, and the area-weighted reflectance of the interior surfaces is taken to be 0.4.It is considered that to achieve appropriate daylighting for a school atrium, a minimum average daylight factor of 7% should beprovided.

ROOF GLAZING

The area of roof glazing required to obtain anaverage daylight factor of 7% at the bottom ofthe atrium can be determined by adapting thecalculation formula and method used inAppendix 8.2 for the classroom windowglazing. A correction factor of 0.8 is appliedfor dirt on the glass.In these circumstances the calculated area ofglazing is approximately 55m2 which could beobtained by a width of 2.1m either side of theridge for the length of the atrium.

CLERESTORY

The area of clerestory required to obtain thesame daylight level can be determined by asimilar calculation to that used above. Acorrection factor of 0.9 is applied for dirt onthe glass.In these circumstances the area of glazing isapproximately 100m2 which would require aclerestory height of 2m for the full perimeterwhich may be difficult to achieve in practicalterms.

SKY GLARE could be troublesome- precautions need to be taken

SUN could be troublesome- precautions need to be taken

SUPPLEMENTATION good for upper levels of adjoining rooms

VISUAL CONTACT good

SKY GLARE could be troublesome- precautions need to be taken

SUN could be troublesome- precautions need to be taken

SUPPLEMENTATION good

VISUAL CONTACT good

73- 73

COMBINED ROOF & CLERESTORY 'SAW-TOOTH' PROFILE


SKY GLARE less troublesome precautionsneed to be taken

SKY GLARE no problem

SUN less troublesome precautionsneed to be taken

SUN no problem

SUPPLEMENTATION good for upper levels of adjoiningrooms

SUPPLEMENTATION good for rooms on south side

VISUAL CONTACT less good VISUAL CONTACT less good

LAY LIGHTS ASYMMETRIC PROFILE

SKY GLARE not troublesome SKY GLARE less troublesome

SUN not troublesome SUN not a serious problem

SUPPLEMENTATION poor SUPPLEMENTATION good for rooms on south side

VISUAL CONTACT limited VISUAL CONTACT good for rooms on south side

74


Al/B1

A2/132

75

ELECTRIC LIGHTING

r'Cl

C2

It is considered that for the electriclighting to achieve the desired visualcharacteristics discussed earlier for aschool atrium, a suitable arrangementwould be to have a general-installationwith a direct/indirect light distributionproviding an illuminance level ofapproximately 400 lux at the atrium floor,and this would be complemented bysome form of accent lighting which couldinclude highlighting displays, plants, etc.For this arrangement to be satisfactory, itis important, as for the daylightingsituation, to ensure that the majority ofsurfaces, and in particular for the electriclighting, the underside of the roof, have ahigh reflectance value. In selecting theequipment, it is necessary to consider itsease of maintenance, including access to itfor this purpose, so that its performanceremains high.

Three schemes for the electric lightinginstallation are outlined below, with somecalculation details for scheme A beinggiven. The dimensions of the atrium spaceare as used for the daylighting study.

Scheme A. Suspended luminairesFor the main lighting, it is proposed touse high pressure metal halide lamps(MBIF): these have good colourrendering properties with a white colourappearance, high efficacy and long life.They would be housed in luminaires

z),

C3

providing a 'Direct/Indirect' lightdistribution, at a mounting height of 5mabove the floor. Using 400 watt MBIFlamps (average light output = 26,000lumens), an estimated utilisation factorU.F. of 0.35 and a one year maintenancefactor M.F. of 0.8:

Number of luminaires =

Illuminance x Area = 8Lamp light output x U.F. x M.F.

A suitable arrangement would be tosuspend the luminaires in pairs (Al) onthe long axis of the atrium, an opticalsystem providing an asymmetricdownward light distribution, and theGlare Index restricted to be less than 19.A 'rise and fall' suspension system wouldfacilitate maintenance.

Additional general lighting (A2) wouldbe provided by wall, surface-mounteddiffuser luminaires equipped withcompact fluorescent lamps. (SL, PL, 2D,2L) with some light on to the wall surfacebehind: these luminaires should beinstalled in circulation spaces.

Accent lighting would be formed bydisplay screens employing low wattagetungsten halogen reflector lamps(TH(M)) which would be mounted onthe screens.

81

Scheme B. Column-mountedluminairesThis arrangement is similar to that forScheme A but with the pairs of luminairesfor the metal halide lamps mounted oncentrally installed columns at the same 5mheight (B1). These columns at floor levelwould be within planting or seating areas,and if necessary be hinged at the base sothat the luminaires could be loweredfor maintenance.

The additional general lighting and theaccent lighting would follow the patternin Scheme A, but the lower part of thecolumns could now form the basis for thedisplay lighting.

Scheme C. Perimeter-mountedluminairesThe direct component of the mainlighting is provided by wall-mountedprismatic refractor luminairesincorporating a reflector (C1) andequipped with 250 watt high pressuremercury discharge tubular metal halidelamps (MBI). The indirect componentutilises the same type of lamp installed inasymmetric reflector floodlights (C2),

76

their light falling on the adjacent part ofthe underside of the roof. Recesseddownlights (C3) using compactfluorescent lamps are used in this schemeto illuminate circulation spaces wherethere is a soffit. Wall mounted generallighting (A2) as in Scheme A, is usedwhere there is no soffit. The displaylighting would be the same as thatmentioned in Scheme A for the screens.

It is important in the selection of allitems of lighting equipment to ensurcthat there is good integration with theatrium design as a whole.

Actual photometric data provided bymanufacturers for their luminaires should,of course, be used in any practical design.

GENERAL

When the various factors described inrelation to sunlight, daylight and electriclight are taken into account, a well-litatrium space can contribute appreciably tothe environment of a school, both byproviding a visual centre and bycomplementing the view fromsurrounding areas.

The definitions and explanations given inthis glossary are based on British Standard4727: Part 4: Glossary of terms particularto lighting and colour, and on the fourthedition of the International LightingVocabulary (CIE 17.4:1987) issuedjointly by the Commission Internationalede L'Eclairage and the InternationalElectrotechnical Commission. Thesedocuments should be consulted if moreprecise definitions are needed.

adaptationThe process which takes place as thehuman visual system adjusts itself to thebrightness or the colour of thevisual field.

average daylight factorThe spatial average of daylight factorsover a reference plane or planes.(For design purposes in this document, itis the average over a horizontalworking plane).

ballastCurrent limiting device found in aluminaire.

CIE standard overcast skyCompletely overcast sky for which theratio of its luminance Le at an angle ofelevation 0 above the horizon to theluminance Lz at the zenith is assumed tobe given byLe = 1,, (1 + 2 sin0)/3

colour appearanceA term used of a light source. Objectivelythe colour of a truly white surfaceilluminated by the source. Subjectively,the degree of warmth or coolnessassociated with the source colour.

colour renderingA general expression for the appearance ofsurface colours when illuminated by lightfrom a given source compared,consciously or unconsciously, with theirappearance under light from somereference source.

colour rendering indexA measure of the degree to which thecolours of surfaces illuminated by a givenlight source conform to those of the samesurfaces under a reference illuminant,suitable allowance having been made forthe state of chromatic adaptation(see Appendix 3).

contrastSubjectively this term describes thedifference in appearance of two parts of avisual field seen simultaneously orsuccessively. The difference may be one ofbrightness or colour or both.

correlated colour temperatureThe temperature of a full radiator thatemits radiation having a chromaticitynearest to that of the light source beingconsidered. The unit is the kelvin, K.(see Appendix 3).

daylight factorThe illuminance received at a pointindoors, from a sky of known or assumedluminance distribution, expressed as apercentage of the horizontal illuminanceoutdoors from an unobstructed hemisphereof the same sky. Direct sunlight isexcluded from both values of illuminance.(daylight factor = sky component +externally reflected component +internally reflected component).

direct glareGlare caused when excessively bright partsof the visual field are seen directly, eg,lamps which are inadequately shielded.

directional lightingLighting designed to illuminate an objector surface predominantly from somepreferred direction.

disability glareGlare which impairs the ability to seedetail without necessarily causing visualdiscomfort.

discomfort glareGlare which causes visual discomfortwithout necessatily impairing the abilityto see-detail.

Glossary

77

Glossary

downward light output ratioThe ratio of the total light output of aluminaire below the horizontal understated practical conditions to that of thelamp or lamps under reference conditions.

externally reflected component ofdaylight factorThe illuminance received directly at apoint indoors from a sky of known orassumed luminance distribution afterreflection from external reflectingsurfaces, expressed as a percentage of thehorizontal illuminance outdoors from anunobstructed hemisphere of the same sky.Direct sunlight is excluded from bothilluminances.

flickerImpression of regular fluctuations ofbrightness or colour.

glareThe discomfort or impairment of visionexperienced when parts of the visual fieldare excessively bright in relation to thegeneral surroundings.

glare hidexA numerical index calculated according toCIBSE Technical Memorandum TM 10.It enables the discomfort glare fromlighting installations to be ranked in orderof severity and the permissible limit ofdiscomfort glare from an installation tobe prescribed quantitively (Limiting GlareIndex).

illuminanceThe luminous flux density at a surface, ie,the luminous flux incident per unit area(lumens per square metre (Im/m2) orlux). [This quantity was formerly knownas the illumination value or illuminationlevel.]

illuminationThe process of lighting an object orsurface.

internally reflected component ofdaylight factorThe illuminance received at a pointindoors from a sky of known or assumed

luminance distribution after reflectionwithin the interior, expressed as apercentage of the horizontal illuminanceoutdoors from an unobstructedhemisphere of the same sky. Directsunlight is excluded from bothilluminances.

light output ratioThe ratio of the total light output of aluminaire under stated practicalconditions to that of the lamp or lampsunder reference conditions.

luminaireAn apparatus which controls thedistribution of light given by a lamp orlamps and which includes all thecomponents necessary for fixing andprotecting the lamps and for connectingthem to the supply circuit. Luminaire hassuperseded the term lighting fitting.

luminanceThe physical measure of the stimuluswhich produces the sensation ofbrightness measured by the luminousintensity of the light emitted or reflectedin a given direction from a surfaceelement, divided by the area of theelement in the same direction. The SIunit of luminance is the candela persquare metre (cd/rn2).

luminous efficacyThe ratio of the luminous flux emitted bya lamp to the power consumed by thelamp (lm/W), this term is known aslumens/lamp watt. When the powerconsumed by control gear is taken intoaccount, this term is sometimes known aslamp circuit luminous efficacy and isexpressed in lumens/circuit watt.

luminous fluxQuantity of light emitted by a source, orreceived by a surface. The SI unit ofluminous flux is the lumen (Im).

luminous intensityA quantity which describes the power of asource or illuminated surface to emit lightin a given direction. It is the luminousflux emitted in a very narrow cone

78 84

containing the given direction divided bythe solid angle of the cone. The SI unit ofluminous intensity is the candela (cd)equal to one lumen per steradian.

maintained illuminanceThe minimum illuminance which shouldbe provided at all times through the lifeof an installation: it takes into accountcleaning schedules for room surfaces andluminaires, and lamp output depreciationwith time.

no-sky lineThe locus of points in the reference planedelineating the area from which no skycan be seen.

reflectanceThe ratio of the luminous flux reflectedfrom a surface to the luminous fluxincident on it.

reflected glareA term used to describe various visualeffects, including reduction of contrast,discomfort and distraction, produced bythe reflection of light sources or otherbright areas in glossy or smooth surfaces.

sky component of daylight factorRatio of that part of the daylightilluminance at a point on a given planewhich is received directly through glazingfrom a sky of assumed or knownluminance distribution to the illuminanceon a horizontal plane due to anunobstructed hemisphere of this sky.Direct sunlight is excluded from bothilluminances. Usually expressed as apercentage.

spacing/height ratioThis ratio describes the distance betweenluminaire centres in relation to theirheight above the working plane.

specularityThe specular quality of a reflection as in amirror, as opposed to a diffuse reflectionfrom a matt surface in which theluminous flux comes from manydirections none of which predominates.

standard maintained illuminanceThe maintained illuminancerecommended for the assumed standardconditions of the application.

transmittanceThe ratio of luminous flux transmitted bya material to the incident luminous flux.

uniformity ratioThe ratio of the minimum illuminance tothe average illuminance over a given area,usually a horizontal working plane.ORThe ratio of the minimum daylight factorto the average daylight factor over a givenarea, usually a horizontal working plane.

upward light output ratioThe ratio of the total light output of aluminaire above the horizontal understated practical conditions to that of thelamp or lamps under reference conditions.

utilisation factorThe proportion of the luminous fluxemitted by the lamps which reaches theworking plane both directly andby reflection.

8 5

Glossary

79

Notes

06

The Chartered Institution of Building ServicesEngineers (CIBSE)Code for Interior Lighting, 1994.

Window Design: Applications Manual AM2, 1987.

Calculation of Glare Indices. TechnicalMemorandum TM10, 1985.

Emergency Lighting. Technical MemorandumTM12, 1986.

Libraries: Lighting Guide, 1982.

The visual environment for display screen use:Lighting Guide, LG3, 1996.

Sports: Lighting Guide, LG4, 1990.

The Visual Environment in Lecture, Teaching andConference Roomt Lighting Guide LG5,1991.

The Outdoor Environment Lighting Guide LG6,1992.

CIBSE publications are available from CIBSE,Delta House, 222 Balham High Road, London,SW12 9BS, Tel: 0181 675 5211,Fax: 0181 675 6554.

British Standards InstitutionBS 5266: Emergency Lighting.Part 1: 1988. Code of practice for the emelgencylighting of premises other than cinemas and certainother specified premises used for entertainment.

BS 8206: Lighting for Buildings.Part 1: 1985. Code of Practice for artificiallighting.Part 2: 1992. Code of Practice for daylighting.

BSI publications are available fromBSI Publications, Linford Wood, Milton Keynes,MK14 6LE

Building Research EstablishmentBRE Digest 232: 1979. Energy conservation inartificial lighting.

BRE Digest 272: 1985. Lighting controls anddaylight use.

BRE Digest 309: 1986. Ertimating daylight inbuildings, Part 1.

BRE Digest 310: 1986. Estimating daylight inbuildings, Part 2.

Daylighting as a passive solar energy option : anassessment of its potential in non-domesticbuildings, V.H.C. Crisp, P.J. Littlefair, I. Cooperand G. McKennan. BRE Report (BK129), 1988.

BEST COPY AVALAB

Bibliography

The energy management of artificial lighting use,V.H.C. Crisp and G. Henderson. LightingResearch and Technology, 14(4), 193-206 (1982)

Information Paper IP6/96: People and LightingControls.

Designing buildings for daylight, James Bell andWilliam Burt, BR288, 1995,ISBN 1 86081 026 8.

Site layout planning for daylight and sunlight aguide to good practice, P.J.Littlefair, BR209, 1991,ISBN 0 85125 506 X.

Good Practice Guide 160, Electric lightingcontrols a guide for designers, installers and users,1997, from BRECSU.

General Information Report 25, Daylighting forsports halls, Two case studies, 1997, fromBRECSU.

Good Practice Guide 245, Desktop guide todaylighting for architects, 1998 from BRECSU.

Introduction to Energy Efficiency, Building EnergyEfficiency in Schools, A guide to the Whole SchoolApproach, BRECSU 1996

BRE publications: Tel: 01923 664444,Fax: 01923 664010.BRECSU Publications: Tel: 01923 664258

Department for Education and EmploymentBuilding Bulletin 9: Colour in School Buildings(4th Edition), 1969. Out of print (Photocopyavailable from The Stationery Office).

Building Bulletin 73: A Guide to Energy EfficientMaintenance and Renewal in EducationalBuildings, ISBN 0 11 270772 6, HMSO 1991.

Building Bulletin 78: Security Lighting,ISBN 0 11 270822 6, HMSO 1993

Building Bulletin 87: Guidelines forEnvironmental Design in Schools,ISBN 0 11 271013 1,The Stationery Office 1997

Other sources.Glare from windows: current views of the problem:P. Chauvel, J.B. Collins, R Dogniaux and J.Longmore. Lighting Research and Technology,14(1), 31-46, (1982).

Fluorescent lighting and health: RT. Stone. LightingResearch and Technology, 24(2), 55-61, (1992).

Building Sight, Peter Barker, Jon Barrick,Rod Wilson, RNIB, ISBN 011 701 9933,HMSO, 1995, £35.

The art and science of lighting: A strategy forlighting design: D.L.Loe and E.Rowlands.Lighting Research and Technology 28(4),p.153-164, 1996.

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This building bulletin guidesarchitects and engineers throughthe process of lighting design inthe context of the recommendedconstructional standards forschools and the various types ofspaces and activities found inschools. It identifies thedetermining factors of goodlighting design as architecturalintegration, task and activitylighting, visual amenity, cost,maintenance and energy efficiency.It describes the calculationmethods and design tools that canbe used at the early stages of aproject and shows through theoryand examples how to achieve asynthesis between daylight andelectric lighting. Tables of lampsand luminaires give an appreciationof the types of lighting available,their energy efficiency, colourrendering and othercharacteristics.

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