5 bs ii electricity unit ii 2012 five

7/28/2019 5 Bs II Electricity Unit II 2012 Five

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AR 4.5 BUILDING SERVICES - II: ELECTRICAL SERVICES:

Unit V:

Lighting Calculation: NBC standards, nominalillumination levels in building interiors, lux, lumen,intensity, lighting schemes.


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ILLUMINATION AND LUX: What is the method for calculating illumination ?The problem of the Architect / Lighting Designer at thefunctional level is to determine how many lights andwhere to place them to get the correct level of illuminationfor a given activity.

What do we understand by LUX ?The lux (symbol: lx) is the SI unit of illuminance andluminous emittance, measuring luminous flux per unitarea. It is used in photometry as a measure of theintensity, as perceived by the human eye, of light that hitsor passes through a surface. It is analogous to theradiometric unit watts per square metre, but with thepower at each wavelength weighted according to theluminosity function, a standardized model of human

visual brightness perception. In English, "lux" is used inboth singular and plural.


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ILLUMINATION AND LUX: One lux is equal to one lumen per square metre:

A lux meter for measuring illuminances in work places.
http://en.wikipedia.org/wiki/File:Lux_meter.jpg


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ILLUMINATION AND LUX: One lux is equal to one lumen per square metre:

In other words .. LUX = Level of Illumination.

OR

LUX (lx) = Lumens / Sq.M.Level of Illumination ?

LUMEN METHOD:This method works perfectly in most cases where theheight of the ceiling is within 3000 mm from floor level,the Working Plane is between 750 to 1000 mm and

proportions of the area are proper.


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ILLUMINATION AND LUX: How To Calculate Lux ?

How do I calculate lux - the formula?

Lux level = total light output (lumens) / area (square

meters)

Total Light Output = lumens per fixture * number offixtures

Therefore

Number of Fixtures = (Lux level * area) / lumens per

fixture


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ILLUMINATION AND LUX:

Every Lamp has certain Lumens.

You need to look up the manufacturer data for your lightfitting to get the lumens per fixture.

S.No. Type of Lamp. Lumens Output.1. 36 W Tube Light. 2400 Lumens.

2. 60 W GLS Lamp. 600 Lumens.3. 10 W CFL. 600 Lumens.


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ILLUMINATION AND LUX: Example:Assume a Room size of = 10000 x 8000 x 3000 = 80 Sq.M.Area = 80 Sq.M.

Suppose the desired lux level or Illumination = 300 lx.

Total Lumens required = 300 x 80 = 24,000 lumens.

Assuming that you are using 36W Lamp (FTL) and thesame has 2,400 lumens illumination.

Number of Fixtures required = 24,000 / 2400 = 10 Nos.So you need 10 Nos. of 36W Tube Light Fittings.


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ILLUMINATION AND LUX: What we did above is still not sufficient as there arecertain Correction Factors involved. There are basicallytwo Correction Factors i.e., Utilization Factor = UF andMaintenance Factor = MF.UTILIZATION FACTOR: (UF)

This may be due different reasons viz., RoomReflectance's, Dimensions etc.,

The utilization factor (UF) is a Direct ratio. This is theproportion of the downward luminous flux that reachesthe work area directly without reflection. It depends onthe shape of the room. The Direct ratio has a low valuewith a tall narrow room (small RI) and a high value for awide room (large RI).


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ILLUMINATION AND LUX: The light distribution from the luminaries. Luminariesthat emit light through a larger solid angle will generallyhave a smaller direct ratio that luminaries that emit lightin a narrower beam.

There exist data sheets of UF for rooms of different shapesand luminaries of a common type.

Catalogues of luminaries often provide data sheets of UFfor rooms.

Normally we take 0.8 as the Utilization Factor.


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ILLUMINATION AND LUX: This utilization factor is somewhat more complicated todetermine than the maintenance factor.

The utilization factor will depend on the following:

The luminarie properties. One needs the light output ratio(LOR). How much of the light emitted by the lampsactually leaves the luminarie? An enclosed lamp in aluminarie with low reflectivity will have a smaller LORthan a naked lamp.

The light emitted downwards will probably reach thework area without reflections. However light emittedupwards can only reach the work area after reflection(s)from surfaces.


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ILLUMINATION AND LUX: The utilization factor will depend on the following:The reflectance of the room surfaces. Are the surfaces(walls, ceiling) light or dark in color?(A color with strong chroma does not reflect other colors).Reflectance's are available from manufacturers of paintsand furniture finishing's.It is usual to make the reflectance of the ceiling highest,walls slightly lower and the floor darker.Reflectance's of desks should be 20-40%. Do not choosevery dark wood, or bright surfaces.The geometric proportion of the room. The geometricshape of the room will affect the UF. A factor called theroom index (RI) is defined from the horizontal verticalareas of the room.


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ILLUMINATION AND LUX: MAINTENANCE FACTOR: (MF)It is also known as LLF OR Light Loss Factor. This may bedue different reasons viz., Time, Temperature, Cleanlinessetc.,The maintenance factor gives an estimate of how lightingconditions will deteriorate through use.Some factors are: Dust and dirt inside luminaries surfaces. Aging of light bulbs emitting less light.

Cleaning of room surfaces, e.g. ceiling.Normally we take 0.75 to 0.8 as the Maintenance Factor.


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ILLUMINATION AND LUX: Coming back to our earlier Example where we said thatwe need 10 Nos. of 36W Tube Light Fittings.Now with application of UF and MF it will be as follows:

No. of Fixtures = 10 / 0.8 x 0.8 = 15.625 i.e., 16 Nos.

But practically many times to maintain the balance wemay use upto 12 Nos. of fixtures also.

FormulaforNumber ofFixtures.

Lux x Area / 300 x 80 / 15.625Lumen

Output x MFx UF

2400 x 0.8 x 0.8


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LIMITATION OF LUMEN METHOD: There are certain limitations to this method, but all saidand done this works perfectly for 90% of the installationswhere the parameters are within the limits.Height is not considered.Fixtures or luminaries changes are not considered. (Polarcurve etc.,)Room Reflectance's are not considered.It does not distinguish between different fixture behaviorsi.e., point source or linear source etc.,

For this there is one more complicated method known asPOIINT BY POINT METHOD . This is more specific forexperts in Lighting Design and detailing.


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GLARE: The control of glare:Glare occurs in both natural (daylight) and in interiorlighting situations. It is most annoying in the interior lightenvironment where the lighting is under human control.The glare annoyance depends on a number of factors

In a supermarket people are on the move and not alwayslooking in same direction.

In a classroom students are usually looking in a fixeddirection.

In a classroom, students are reading, this is a moderatelydifficult visual task.

Students are fixed for a long period of time.Standards for glare depend on the use of the visualenvironment.


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GLARE:

The glare index

There is quantity called the discomfort glare constant ( g)which is:

Glare index. Reaction.

0 - 10 Imperceptible

10 - 16 Noticeable

16 - 22 Acceptable 22 28 Uncomfortable

> 28 Intolerable


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GLARE: More visually demanding tasks with high illuminancelevels are less tolerant of glare.

(At present time, do not require you to calculate the glareindex, require you to know what it is and when it is mostimportant to eliminate.)

Limiting GI

Occupations

16 Drawing offices, very fine visual inspections.

19 Offices, libraries, keyboard and VDT work(reflections from screen).

22 Kitchen, reception area, fine assembly.

25 Stock rooms, assembly line for easy tasks.

28 Indoor car park, rough industrial work.


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GLARE: TIPS TO CONTROL GLARE:Keep luminance of source down. Use of diffusers andlouvres. Cutting down glare also cuts down total lightemitted and this problem also needs to be tackled.Reflected light can also be a source of glare.Keep luminaires out of field of view. Highceilings are good.Keep area of source small.To cut down glare, avoid luminaires that emit light tosides (e.g. battern luminaire with a diffuser at the sides),light emitted more in downward direction avoids visual

discomfort.


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GLARE: UPLIGHTING:In this form of lighting, lighting is directed upwards to theceiling. Reflected light from the ceiling provides thegeneral illumination in the room.Advantages, elimination of glare is one of the majoradvantages.Re-introduction driven by the increasing use ofcomputers.Disadvantage, it is somewhat inefficient. Low conversionof electrical energy into usable light.If the Ceiling is quite bright, it will have less visualemphasis on other areas of room, furniture, floors.To get an even illumination on the ceiling requires thatyou have a high ceiling.


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GLARE: UPLIGHTING:You either like it or not. It is possible to use combinationsof direct diffuse and indirect lighting.Illumination can be calculated using lumen method inconjunction with transfer function tables.Need to maintain a uniform illumination on ceiling.Eliminates light hot-spots that can result in glare.Harder with low ceiling.Besides less glare, concentrated beam downlights result in

darker ceiling. This can result in an oppressivepsychological effect.


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LIGHTING STANDARDS: What are the legal requirements for office lighting? Isthere a legal requirement for daylight?The only legal requirements are 'sufficient and suitable'and similar wording in health and safety legislation. Thereis no absolute legal requirement for daylight, but it is arequirement that it be provided if practicable. Various

guidance documents suggest good practice, but are notthemselves mandatory.

What is the recommended lighting level for offices?The Code for Lighting recommends a maintained

illuminance of 500 lux for general offices (e.g. writing,typing, reading, data processing, etc.) and for CAD workstations and conference/meetings rooms. Where the maintask is less demanding, e.g. filing, a lower level of 300 lux

is recommended.


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ILLUMINATION LEVELS AND LIMITING GLARE :

The table following lists illumination levels suitable for arange of situations: the quality of these levels could beinfluenced by glare and an acceptable limiting index isalso shown. The glare index is calculated by consideringthe light source location, the luminances of the source, the

effect of surroundings and the size of the source.

Glare indices for artificial light range from about 10 for ashaded light fitting having low output to about 30 for an

un shaded lamp.


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ILLUMINATION LEVELS AND LIMITING GLARE : As seen from this illustration, various basic decisions haveto be made concerning lighting objectives and whether thesystem involves daylight, electric light or a combinedsystem. With electric or combined systems, furtherdecisions must be taken concerning the way light isdistributed by particular fittings, and upon their positions

relative to each other as well as in relation to the surface tobe illuminated. As with day lighting, light-coloured andhighly reflective room surfaces help to provide moreillumination from the same amount of energy source itpreserves the luminance effect of the light source.


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Location. Illuminance. (lx) Limiting Glare Index.

Entrance Hall. 150 22

Staircase. 150 22Corridors. 100 22Outdoor Entrances. 30 22Casual Assembly Work. 200 25

Rough / Heavy Work. 300 28Medium Assembly Work. 500 25Fine Assembly Work. 1,000 22Precision Work. 1,500 16

General Office Work. 500 19Computer Room. 750 16Drawing Office. 750 16Filing Room. 300 22Shop Counter. 500 22

Super Market. 500 22


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Location. Illuminance. (lx) Limiting Glare Index.

Class Room. 300 16

Laboratory. 500 16Public House Bar. 150 22Restaurant. 100 22Kitchen. 500 22

Dwellings:Living Room. 50 NA.Reading Room. 150 NA.Study Room. 300 NA.

Kitchen. 300 NA.Bed Room. 50 NA.Hall. 150 NA.Library Reading Area. 200 19Library Tables. 600 16

Library Counter. 600 16


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LIGHTING LEVELS : (lx) Activity. Area.

100 Casual seeing Corridors, changing rooms, stores

150 Some perception of detail Loading bays, switch rooms, plantrooms

200 Continuously occupied Foyers, entrance halls, dining rooms

300 Visual tasks moderately easy Libraries, sports halls, lecturetheatres.

500 Visual tasks moderately difficult General offices, kitchens,laboratories, retail shops.

750 Visual tasks difficult Drawing offices, meat inspection,chain stores.

1000 Visual tasks very difficult General inspection, electronicassembly, paint work, supermarkets.

1500 Visual tasks extremely difficult Fine work and inspection, precisionassembly.

2000 Visual tasks exceptionallydifficult

Assembly of minute items, finishedfabric inspection.


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ELECTRICAL FORMULAS: Demand for Power (kW) = System Input Wattage (W) 1,000

Energy Consumption (kWh) = System Input Wattage (kW)x Hours of Operation/Year

Hours of Operation / Year = Operating Hours / Day xOperating Days / Week x Operating Weeks / Year

Lighting System Efficacy (Lumens per Watt or LPW) =System Lumen Output Input Wattage

Unit Power Density (W/ Sq.M.) = Total System Input

ELECTRICAL FORMULAS


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ELECTRICAL FORMULAS: Wattage (W) Total Area (Sq. m.)

Watts (W) = Volts (V) x Current in Amperes (A) x PowerFactor (PF)

Voltage (V) = Current in Amperes (A) x Impedance(Ohms) [Ohm's Law]

ECONOMIC FORMULAS


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ECONOMIC FORMULAS: Simple Payback on an Investment (Years) = NetInstallation Cost Annual Energy Savings.

5-Year Cash Flow = 5 Years - Payback (Years) x AnnualEnergy Savings.

Simple Return on Investment (%) = [Annual EnergySavings Net Installation Cost ] x 100

DESIGN FORMULAS


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DESIGN FORMULAS: Footcandles & Lumens

Footcandles (fc) = Total Lumens (lm) Area in Square Feet

1 Lux (lx) = 1 Footcandle (fc) x 10.76

Lux = Total Lumens Area in Square Meters

SUNLIGHT


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SUNLIGHT: 400 lux: Sunrise or sunset on a clear day.

1,000 lux: Overcast day.

10,00025,000 lux: Full daylight (not direct sun)

32,000130,000 lux: Direct sunlight.

5 bs ii electricity unit ii 2012 five

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