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Module 1 Illumination Engineering Basics Version 2 EE IIT, Kharagpur 1

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Page 1: Illumination Engg

Module 1

Illumination Engineering Basics

Version 2 EE IIT, Kharagpur 1

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Lesson 1

Introduction Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

• State the need for Illumination. • Define good Illumination. • State what comprises an electric utility? • List standard voltage levels. • State need for high voltages for transmission.

Course Overview

• Radiation and colour. • Eye and vision. • Different entities of illuminating systems. • Light sources: daylight, incandescent, electric discharge, fluorescent, arc lamps and

lasers. • Luminaries, wiring, switching and control circuits. • Laws of illumination; illumination from point, line and surface sources. • Photometry and spectrophotometry, photocells. • Environment and glare. • General illumination design. • Interior lighting – industrial, residential, office departmental stores, indoor stadium,

theater and hospitals. • Exterior lighting – flood, street, aviation and transport lighting, lighting for displays and

signaling – neon sign’s, LED – LCD displays beacons and lighting for surveillance. • Utility services for large building/office complex and layout of different meters and

protection units. • Different type of loads and their individual protection. • Selection of cable/wire sizes; potential sources of fire hazards and precautions. • Emergency supply-stand by and UPS. • A specific design problem on this aspect.

Introduction Light by definition connotes Electromagnetic radiation that has a wavelength in the range from about 4,000 (violet) to about 7,700 (red) angstroms and may be perceived by the normal unaided human eye. In fact in the prehistoric days, all human activities were coordinated with Sunrise and Sunset. Today, in principle activities are carried out round the clock. All this is made possible because of Artificial Lighting systems. The lighting systems comprise of a source employing any physical phenomenon among Incandescence, Electrolumniescence or Flourescence. Some control scheme and a Luminaire. In fact all this has lead to a class of professionals called Lighting Engineers or Illumination Engineers. Unlike other group of professionals they need to be adept at not only at exact sciences of Maths, Physics, Chemistry; but be wary of Physiology and Psychology of users (like a medical professional); have good aesthetic sense and economically utilize resources (like an architect video Fig. 1). Efficacy of these systems is talked in terms of Illuminance per Watt of energy consumed. Efforts are on to reduce energy conmsumption yet have efficient Illumination to enhance productivity. Need less

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to mention that all these sources employ electrical energy. Trend these days is to employ, modern electronic controls together with energy efficient lamps. These aspects are borne in mind, right from the planning stage of a building. As electrical energy is being used for the purpose, it becomes important for Illuminating Engineer to come up with an integrated system for the complete electrical system of a building.

Usefulnessto

Humanity

Math ChemistryPhysics

Economics

Art (Aesthetic point)

PhysiologyPsychologyMedicine

Illumination Engineering

Architecture

Fig. 1 Professions-sciences-usefulness relationship.

1. Necessity of Illumination Humans depend on Light for all activities. Light is a natural phenomenon, very vital for existence, which is taken for granted. In fact, Life involves day night cycles beginning with sunrise and ending with sunset. Pre-historic man had activities limited only to day time. Artificial light enables extended activity period employing in an planned optimized manner, minimizing the resources. Vision is the most important sense accounting for 80% information acquisition for humans. Information may be acquired through sun/moon light (direct/ reflected) or by using artificial light (closest to natural light). Before we go any further, it is worth looking at Teichmuller’s definition for lighting. “We say the lighting is good, when our eyes can clearly and pleasantly perceive the things around us”. Therefore Artificial light should be Functional and pleasant both Physiologically and Psychologically. This is often achieved employing multiple sources. It must be borne in mind that the sources should be economic and energy efficient. As all of us are aware, all sources today employ electrical energy. Electrical energy is supplied as a.c. (alternating current) or d.c. (direct current). Usually electric power supply is a.c. in nature, either single phase or three phase. It must be borne that close circuit is a must for current flow. As it is well known losses exist in all electrical circuits or lines.

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By definition Losses = i2 R, where i = line current in A, R = line resistance in Ω longer the line higher the resistance and higher level. Thus for a particular power level current decreases with increase in voltage i.e. p = v x i (instantaneous power). Hence, losses are minimized by supplying at higher voltages. Normal sources of electrical energy are either hydro or thermal (coal based or nuclear). Usually power stations are located very far from load centers. Therefore, power is transmitted at high voltages. It may be mentioned that, standard levels of power transmission being 132, 220, 340, 400, 735, 765, 1000 kV ac. HVDC or High Voltage Direct Current transmission is also fast catching up as an alternative.

Fig.2 shows a single line diagram of a typical Power System with all its components.

X’mission line 132/220/400 kV

400 V

~Generator11/

33 kV

Fig. 2 Typical Power System

Distribution line 66/33/11kV

We know that load is always unbalanced for a practical 3-phase system. Fig 3 shows the waveform of a 400 V 50 Hz a.c supply. Here, 400 V, 3 phase, 50 Hz connotes that supply is three phase a.c. at a frequency of 50 Hz with a line to line voltage of 400 V rms, which translates to 564 V peak value.

564

V

1tmsms

2

Fig. 3 Waveform of 400V, 50Hz a.c supply

In view of the fact that artificial Illumination employs electrical energy in a.c form, next, we address each fundamentals of a.c generation.

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Fundamentals of a.c Generation Single Phase AC Generation Fig 4: shows Loop AB carried by a spindle rotated anti clockwise in a uniform magnetic field due to poles NS. This explains the single phase a.c generation In this Coil ends C1 and C2 are brought out through (but insulated) and connected to two carbon brushes E1 E2 across which E m f is developed when connected to load ‘R’. When plane of coil is horizontal no E.m.f. is developed as sides A and B do not cut any flux. If v be the peripheral velocity of each side in m/s AL – represents v in Fig. 5.

Slip Rings

As rotating coil is rotated through an angle ‘θ’ from horizontal resolving AL , we have , AM – Horizontal Component, AN – Perpendicular Component.

∵ oMLA = 90 - MAL = MAO = θ AM = AL sinθ = v sinθ

AN = AL cosθ = v cosθ We know E.m.f generated in ‘A’ is only due to AM perpendicular to magnetic flux density

- ‘B’ - If ℓ be the length of the sides A and B

∴ e.m.f generated on one side = Bℓv sinθ volts …………………..( 1 )

R

N

B ω

A

S

Fig. 4 Single Phase Generation

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A

o

b

θ

L

B θ

0

M

L

A

N

θ

90°

Fig. 5 Single Phase Generation

• Total e.m.f. generated = 2Bℓv sinθ ….( 2 )

if θ = 90°. Coil is vertical. E.m.f. generated is maximum.

Em = 2Bℓv ………………………………..( 3 ) or in other words

∴ e = Em sinθ ……………………………...( 4 ) Let b = breadth of loop n = speed of rotation in r.p.s then v = πbn m/s ∴ Em = 2πBbℓnv = 2πBAn = A = Loop area If coil of ‘N’ turns replaces the loop Em = 2πBAnN …………………………..( 5 ) e = Emsinθ = 2πBAnNsinθ …………... (6) Generation of 3 phase E.m.f.

• Just as we saw how single phase ac is generated by rotating a coil through a magnetic field. If three similar loops fixed to each other at 120° on a common spindle and rotated as shown in Fig 6.

• Connected to slip rings – on the shaft • R, Y, B on there coils – termed finish and R1, Y1, B1 are termed start when • Rotated anti clock wise at uniform speed in magnetic field due to NS. • For the position in figure (1) E.m.f. in RR1= 0 • When moved by 90° (2) – E.m.f. is RR1 ≈ max generated e.m.f. in YY1 and BB1 have

same amplitude as in RR1 but lag by 120° and 240° respectively. Generated voltages in three coils are

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∴ eR = Em sinθ eY = Em sin( θ – 120°) and eB = Em sin( θ – 240°)

Fig.6 Generation of three-phase e.m.f.s.

N S

R

R1

Y

Y1

B

B1

The waveform of the Generated emf is shown in Fig.8

Fig. 7 Loop RR1 at instant of maximum e.m.f.

R R1

Slip-rings for Phase RR1

Finish

Start

N S

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0

+

E.M.F. in RR1 E.M.F. in YY1 E.M.F. in BB1

60° 120° 360°

L

M

Fig. 8 Three Phase ac waveforms.

Next we need to look at how three phase circuits are connected. As already well know Three Phase Connections could be – Delta as shown in Fig 9. R

B

Y

Fig.9 Delta connection.

Where Line Voltages = Phase Voltages. Line Quantities are IR, IY, IB, VB RY, VYB and VBR Phase Quantities are IRY, IYB, IBR, VRY, VYB and VBR. Three phone connection could also be a star as shown in Fig 10.

SB Y

R

Fig. 10 Star Connection.

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Where Line currents = Phase currents. Phase quantities are IR, IY, IB, VRS, VYS and VRS Line quantities are IR, IY, IB, VRY, VYB and VBR Further Loads may be balanced as shown in Fig. 11 What is a balanced load? A Balanced Load is one where Impedance Nature is same in all three phases i.e. equal in both magnitude and Phase and draw equal current in all the three phases. R

B

Y

SB Y

R

Fig. 11 Balanced Loads

Loads may also be unbalanced as shown in Fig. 12 A load if Unbalanced Load when Impedance Nature is not same in all the three phases and draw unequal currents in the three phases .

Z Z

Z

IR

IY

IB

Z

Z Z

IR

IYIB

Fig. 12 Unbalanced Loads

How do we connect the sources to loads. Through lines which are either overhead lines or underground cables. Commonly employed cables are XLPE (Cross Linked Polyethylene) or PILC (Paper Insulated Lead covered), they could be single cored at higher voltages or multi cored at lower voltages. Normally Single storied small buildings are serviced by single phase a.c. i.e. 220V, 50Hz Where as large buildings are serviced by three phase a.c. i.e. 400V, 50Hz. It may be mentioned that sparsely populated, short distances are serviced by distribution at 400 V. In densely populated, vast areas power distribution is at 11 kV / 33 kV. Distribution of power may be through underground (UG) cables or overhead (OH) lines urban localities are serviced by UG cables. Rural settings are serviced by OH lines, where there is a lot of free space.

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Conclusion This Lecture essentially covered need for illumination, and fundamentals of electric utility Lecture Summary

Usefulnessto

Humanity

Math ChemistryPhysics

Economics

Art (Aesthetic point)

PhysiologyPsychologyMedicine

Illumination Engineering

Architecture

Good lighting → our eyes clearly and pleasantly perceive things. Artificial lighting → use some form of physical phenomena. All lighting sources today employ electrical energy.

• Electric Current sources • DC • AC – single phase and three phase.

• Sources of electrical energy – Hydro & Thermal.

X’mission line 132/220/400 kV

400 V

~Generator11/

33 kV

• Load is always unbalanced for a practical 3-phase system.

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Tutorial Questions

• Why do we go for transmission of power at higher voltages?

Because power losses on transmission lines is inversely proportional to the operating voltage

• What are two ways through which power can be distributed?

By underground cables & overhead transmission lines

• How do you decide the distribution voltage level for a particular area?

Sparsely populated short distance distribution – 400V Densely populated vast area distribution – 11/33kV

• What do you mean by 400V, 3-phase in Indian system?

In Indian system, it means 3-pahse 400Vline to line rms voltage at a frequency of 50 Hz.

• When is a load balanced?

When both the magnitude and phase of the load impedances for a 3-phase system are equal

• When do you go for 1-phase & 3-phase supply?

For a single storied small building-1-phase supply For a large building – 3-phase supply

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Module 1

Illumination Engineering Basics

Version 2 EE IIT, Kharagpur 1

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Lesson 2

Radiation Version 2 EE IIT, Kharagpur 2

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Instructional objectives

1. State the Visible Range of light. 2. State the range of light human eye responds to. 3. Define UV radiation. 4. Define IR radiation. 5. List the physical phenomenon employed in artificial lighting. 6. Define color temperature.

Introduction Light is the Radiant Energy that provides visual sensation. It is similar to radiant heat. But has different frequencies and wavelengths. However, Visible Light – spans from 180nm to 700nm wavelength. It must be mentioned that human Eye responds from 380 (violet) to 700nm (red). This becomes necessary for us to understand the suitability of various types of sources of light.

Sunlight

Red 700nm

Violet 380nm

Fig. 1 Spectrum of sunlight when passed through a Prism Fig.1 shows how sunlight splits into various color bands spread over violet to red often termed vibgyor. Energy is spread over this spectrum from the sunlight. Fig. 2 shows the relative energy content of the solar radiation. While Fig. 3 shows the response of human eye to the solar radiation, which is maxima at about 550nm. (Corresponding to yellow green color).

Relative Energy

Germicidal Visible Spectrum

UV

IR Drying Heating Therauptic

f < fredλ >λred

X

380nm 800nmViolet Red λ

f > Fλ

violet < λ violet

500 – 600nm Green Yellow

Fig. 2 Spectral energy Content of sun light. Version 2 EE IIT, Kharagpur 3

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Relative Luminosity

Green

400nmViolet

550nm 720nm Red

λ

Fig. 3 Luminosity Curve of Average Human

W avelength

This being the scenario of natural light, artificial sources are made to produce radiation close to this. Artificial sources employed are Incandescent lamps which depend on temperature of the filaments giving a continuous spectrum and gas or discharge lamps giving a discontinuous – Line spectrum / Band spectrum. Fig. 4 shows the relative energy content of Noon Sunlight, clear blue sky, and an Incandescent lamp. It is seen that the relative energy is peak at about 450nm for blue sky.

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Spectral Energy

Blue sky

200

1.0

As may be seen, most of the energy is of low visual value. Even sunlight has very small portion in highly luminous region. Energy content multiplied Luminosity of eye at a particular wavelength gives the Luminosity of the source. Physical Processes Employed in the artificial sources 1. Incandescence Thermo luminescence is by definition radiation at high temperature. The sources employing this process are Incandescent Lamp, Gas Lamp, (flames and in oil Lamps and wax candles). They lead to a continuous spectrum of radiation. 2. Luminescence – Luminescence Electro luminescence by definition Chemical or Electrical Action on gases or vapour radiation. Here color of radiation depends on the material employed. Usually this process leads to Line or Band Spectrum. 3. Fluorescence Fluorescence is a process in which radiation is absorbed at one wavelength and radiated at another wavelength eg: UV impinging on Uranium – Fluorescent oils. This re radiation makes the light radiated visible.

NOON

400 Violet

500 600 700 Red

λ

160 120 80 40

SUN

.8 .6 .4 .2 R

elat

ive

Ener

gy

y

Lum

inos

it

Lum

inos

ity

in nm

Fig. 4 Spectral Energy Distribution

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4. Phosphorescence Phosphorescence is a process when energy is absorbed at some time and radiated later as glow. Examples of this process are Luminous paints that contain calcium sulfide that lead to Phosphorescence. They produce light Radiation after exposure to light. In practice good efficient lighting is obtained by combining Luminescence and Fluorescence. Fluorescent lamp is Luminescent source of low luminous value activating Fluorescent surfaces which lead to visible radiation. Here intensity depends on gas or vapor involved and phosphor material. However, the temperature of the material play a role in radiation. That is taken up next Color Temperature Radiation Temperature of the materials follow Steafan Boltzman’s Law: W = kT4 …………………….( 1 ) Absolute °k ≈ 5.71x10-12

Its Boltzman’s constant or radiation constant

Say Ambient Temperature is T0 W = k ( T4 – T0

4 ) watts/cm2 ................(2) Thus energy radiated depends on the 4th Power of temperature. So efficiency is high at high temperatures. Fig. 5 shows the variation of radiation with wavelength for a black body. In each curve total area denotes the energy which increases as 4th power of temperature. Rate of increase of radiation is greater as maxima of radiation shifts with temperature. It goes on till 6500 – 7000° K with 43% radiation visible. This relates to an emission of 90 lm/w

4000°k

3000°k

2000°k

1000°k

200 300 λ 800 nm

Fig. 5 Black Body Radiation

0

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Wien displacement law This displacement of maxima is given by wien’s law, expressed as

λm.T = a ( constant ) …………………( 3 ) °k In μm → corresponds to wavelength where radiation is a maxima. a = 2960 for a perfect black body

= 2630 for platinum

Combining, (1) and (3) it results

Wm T-5 = b ( constant ) ……………...( 4 )

Energy corresponding to λm

Wm T -c = constant ……………………( 5 ) C ≈ 6.0

In terms of radiation ability, a body may be called black body or grey body. Black body is one that is not transparent, does not reflect and absorbs all the energy while a Grey Body is one in which energy radiated at each λ is less than that in the case of a black body. That is to say Ratio

of Visible EnergyTotal Energy

(remains same). It remains same or reflects a percentage of energy at each

wavelength. Carbon filament lamp is an example of a grey body. There are bodies of selective radiation also. They radiate less total energy compared to a black body at the same temperature but radiate more energy at certain wavelengths. If this wavelength is in the visible region it will be use full for illumination purpose e.g. Arc Lamps. Thus color temperature is the temperature at which complete radiator ( i.e. a black body ) must be operated to match the color of luminous source. Complete scale of color temperature for various natural and artificial sources is shown in Fig. 6. As may be seen color temperature, for Blue sky it is 25000°K., for a Flourescent Lamp it is 4500°K., for a 500w day light it is 4000°K. and for a Candle flame it is 2000°K. This Lecture has attempted at understanding the nature of solar radiation – natural light source. It is seen to have maximum energy content around 550 nm close to sensitivity of human eye. It has also a addressed the physical process employed in creating artificial illumination. Concludes color temperature an important index of radiation.

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Natural Daylig

ht

Extremely blue clear Northwest sky

DEGREES KELVIN Artificial sources

Blue northwest sky

Blue sky with thin white clouds Blue sky

Uniform overcast sky

Average noon sun

3.30 p.m. 4.30 p.m.

2 hours

1 1/2 hours

1 hour

ins

30 mins

20 mins

Sunrise

40 m

Tim

e af

ter s

unris

e

1 blue and 1 daylight fluorescent lamp

orth skylight filters Available to give a range from

°K

ps

28,00026,00024,00022,00020

Blue glass n

5,400 to 30,000

1 blue and 2 daylight fluorescent lam

,00018,00016,00014,00012,00010,000 8

1 blue and 4 daylight fluorescent lamps

Daylight fluorescent lamps

4 daylight and 1 white fluorescent lamps

,0006,000

5,500

5

3 daylight and 1 white fluorescent lamps

2 daylight and 1 white fluorescent lamps Daylight photoflood

4,500 °K White fluorescent lamp

500-watt Daylight lamp

,000

4

Hig

h ef

ficie

ncy

filam

ent

Ph

otog

raph

ic la

mps

,500

4,000

3,500

Photoflash

150-watt daylight lam

CP Photo lamps - Photofloods

p White fluorescent lamp

Gas-filled

Vacuum

3,000

2

Gen

eral

Se

rvic

e Range of Standard filament lamps

Heat and Drying lamps

Candle flame ,000

2,500

Fluo

resc

ent l

amps

and

var

ious

com

bina

tions

Fig. 6 color Temperature Scale

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Lecture Summary • Light – Radiant energy that provides visual sensation • Human eye can sense – 380nm (violet) to 700nm (red) • Maximal relative energy content of sunlight • Maximal luminosity of human eye • Artificial light sources

• Incandescent Lamp • Gas Discharge Lamp

• Physical Processes employed for artificial lighting

• Incandescence • Luminescence • Fluorescence • Phosphorescence

• Good efficient lighting obtained by combining luminescence & fluorescence.

• According to Stefan’s-Boltzmann Law & Wien’s Law, thermoluminescence, radiation output is directly proportional to the operating temp.

• Color temp. – temp. at which complete radiator (black body) must be operated to match the color of luminous source

Tutorial Questions

• What is the visible range of light? 380nm (violet) to 700nm (red) • What is the maximal relative energy contentof sunlight? 550nm (corresponding to green

light) • Distinguish between incandescent and gas discharge lamps. Incandescent lamps operate

on the principle of incandescence, radiation output depends on operating temperature and it gives a continuous spectrum of light while gas discharge lamps operate on the principle of electroluminescence. The output color depends on the material employed and it gives discontinuous spectrum of light.

• Why is it necessary to operate incandescent lamp at maximum possible operating temperature? Due to the fact that the radiation output is directly proportional to the operating temp. of lamp

• State principle of working of a carbon filament lamp. The ratio of the visible energy to the total energy is constant for all wavelengths.

• State principle of working of an arc lamp? They work on the principle that they emit selective radiations in the visible zone.

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Module 1

Illumination Engineering Basics

Version 2 EE IIT, Kharagpur 1

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Lesson 3

Eye and Vision – I

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Instructional Objectives

1. Identify similarity between eye and camera 2. List the nerve system responsible for adaptation of eye. 3. List factors responsible for visual acuity. 4. State the purpose of good lighting. 5. Define glare. 6. Define Purkinjee effect.

Introduction As already mentioned eye acquires > 80% information acquired by human. We look at the structure and function of eye here. An Eye comprises of Iris, Focusing Lens and Retina. It Resembles – a Camera in general structure and action. Table I shows the similarity between them.

Eye Camera

Iris

Lens

Retina

Shutter

Lens

Film

Table I: Eye Vs Camera

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Fig. 1 shows the structure of eye. As may be seen it consists of:

Fig. 1 Structure of Eye Iris – a diaphragm that regulates amount of light by expanding contracting also know as (Pupil), lens that focuses under the control of ciliary muscles forms image on to the retina. The lens is crystalline in nature. Lastly there is a screen like structure called retina that is holding a lot of - optic nerves – that communicate with the brain. The central region has the greatest sensitivity and is called Fovea. Fovea is the most acute spot of vision where fine details are formed. Rest of the retina is responsible for orientation. The eye communicates through optic nerves located on the retina. They are a system of double nerves called Rods and Cones. Rods are responsible for Dim light / Night vision and Cones are mainly concentrated around or at Fovea and are responsible for form/color sensitivity. As a result vision is of two types; (i) Photopic and (ii) Scotopic Photopic vision involving cone cells and is used for discrimination of fine details for critical observation. They are densely packed and transmits sharp images. The cone cells have low sensitivity below 0.01 ft lamberts and cease to function < 0.001 ft lamberts. It must be mentioned

that by definition 211 lambert is candles / mπ

and 211 ft lambert is candles / ftπ

Scotopic vision involving Rods takes over when brightness < 0.01 ft lambert. This vision has no color discrimination ability. Most images have gray appearance and are viewed as silhouettes lacking sharp details. Eyes have good ability to change from one to other. This shift in Luminosity and ability of eye to adjust is known as Purkinjee effect. Upon increase of intensity of illumination by a decrease in Pupil size producing clearer images with greater and fine details. Pupil diameter varies in the range of 1.2 – 2 mm. Eyes are error free and accommodate very

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well. So eye functions under varying illumination levels by a change in pupil size together with change in Retinal Nerve System (i.e. cones/ rods) as shown in Table II.

Pupil Size or Opening Light Received

Large

Small

Dim Light

High Illumination

Table II Pupil size Vs Light received

Eye is Unconscious to variations in natural light. Thus human eye is A chromatic with a dispersive power little greater than water. Hence for near vision eyes easily focus for blue and tires to focus for red. On the other hand for far vision eye easily focus for Red and strains to focus blue. Table III shows the relationship of Eye opening to lens size, distance of object & color of focus.

Pupil Opening

Lens Shape Object Focus

Large

Small

Flattest

Convex

Distant

Near

Red

Blue For objects distant 1m from the eye, there is no difference in accommodation.

Luminosity of Eye

Bluish Green

≈ 507 nm 550 nm

Cones (YellowGreen Hue)

Lum

inos

ity

Rods

ish

400 500 600 700

λ nm

Fig. 2 Luminosity of Human eye

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Fig. 2 shows the Luminosity curves for Human Eye. As may be seen Cone cells have peak sensitivity around 550nm while Rods have at 500nm.

Remember that seeing is the primary purpose of lighting is to be borne in mind. Good Lighting aims at Prevention or reduction of defective vision at the same time reduces waste of human resources. Improving the conditions of visibility. However, visibility depends on the Size of the object, details of the object, level or Quantity of illumination, contrast or color in brightness and time required (available) for observation. It may appear that requirements are Contradictory as regards size, illumination, contrast and time. For effective deficiency in one of these is to be compensated by the other. So, Visibility depends on efficacy of individual. This in turn depends on eye defects, Eye fatigue which could be optical or physical. It also depends on amount of distraction present. Eye Fatigue are of two kinds Retinal and Muscular. Fatigue is enhanced by glare. Glare by definition is intense illumination in the plane of observation. Source of Glare – Front or behind the plane of attention tires maximum. Best in the plane of attention. Rotating or focusing muscles on the source of glare causes strain and fatigue. Similar fatigue in fact results by reading double impression obtained due to slipping paper in a printing press. After a days work – Pupil is dilated. A nights rest offsets this fatigue. Similarly weekend rest offsets fatigue of the working week. Pupiliary change call for good conditions for seeing. Eye defects arise due to Age Use or Abuse. No doubt Eyes ability to adjust to severe or unnatural conditions – gets injured in the long run. Defective vision may be due to difference in size and location of images by way of Refractory errors. Easy limited tasks lead to no defects. Lower Retinal Sensibility calls for larger pupil diameter and higher illumination levels. Seeing is not instantaneous process. Countless impressions are formed on the retina. Good illumination looks for producing clear and quick images. Lecture Summary

• A human eye resembles a camera in structure and function. • Important parts of a human eye

• Iris / pupil • Lens • Retina

• Types of vision • Photopic (fine image details and color discrimination, due to cone cells). • Scotopic (functions in dim light and no image details, due to rod cells)

• Human eye is achromatic in nature • Dispersive power of human eye is little greater than water • Purkinjee Effect – shift of luminosity and ability of eye to adjust • Maxima sensitivity of

• cone cells – 550nm (yellowish green hue) • rod cells – 507nm (bluish green)

• Good lighting • Prevention of defective vision • Optimization of resources • Improving conditions of visibility

• Visibility depends on – (Observer Issues) • size / details of object

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• level / quality of illumination • contrast / color • available time

• Visibility depends on – (Observer Issues) • efficacy of individual • one’s eye defects • optical / physical fatigue • distraction

• Causes of fatigue – • rotating source • focusing on the source of glare • reading double impression • after a days work pupil is dilated

• A nights rest offsets fatigue due to a days work • Visibility reduces due to eye defects and fatigue • Eye defects caused due to –

• Aging • Use • Abuse

• Good illumination looks for producing clear and quick images

Tutorial Questions

• Which is the most acute spot in human eye?

Fovea as it accounts for the fine details of the image formed.

• What are the two types of vision?

Photopic & Scotopic vision.

• Distinguish between rod cells & cone cells.

Rod cells – scotopic vision, functions in dim light when brightness < 0.01 ft-L, no color discrimination, lack sharp details

Cone cells – photopic vision, ceases to function in dim light, color discrimination, fine details

• How does eye communicate with the brain?

Through a set of optic nerves – the double nerve system i.e. Rods and Cones

• What is the diameter of pupil?

1.2 – 2 mm

• How does eye functions under varying illumination?

By a change in pupil size together with change in retinal nerve system

• Why is red color used for stop signal?

The eye can easily sense red color from a distance due to its large wavelength so that one can get enough time to react & stop.

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Module 1

Illumination Engineering Basics

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Lesson 4

Eye and Vision – II Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

1. What is visual acuity?

2. List qualitative factors responsible for visual acuity.

3. State how the acuity varies with other parameters.

4. State Minimum Illumination requirement for good visibility.

5. Define Chromatic aberration. Today eye tasks are many and for long duration requiring increased illumination. More exacting the task, more illumination is required. Apart from quantity, quality is also important. Illumination affects Physiology and Psychology also. Natural Illumination conditions need to be reproduced. Artificial Illumination characteristics are influenced by the physical characteristics of room or object or illuminating equipment. Color finish of walls or ceiling etc. Quality, Glare, Diffusion, Direction and Composition effect light Distribution. Illumination requirement for equal visibility calls for at least 100 ft candles or more.

Functioning of eye may be assessed by the Visual acuity, ability of Discrimination of brightness and Speed of retinal impression. Factors responsible for visual acuity are Nervous muscular tension, Fatigue of ocular muscles, Normalcy of heart rate, Normal rate of reading, maximal rate of reading, Precision of tasks, Performance in demonstration visual test. Visual acuity is reduced in defective vision. Mainly depends on experience in day light. It bears a Logarithmic relationship.

Visual Activity Vs Illumination As may be seen from Fig.1 visual acuity improves with illumination on a logarithmic basis. Acuity improves by 30% when illumination is increased by 10 times. It may be observed that contrasts sensitivity becomes 280% on increasing illumination 10 times (Fig 2)

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Contrast Sensivity Vs Illumination

Nervous Muscular Tevlion Vs Illumination Fig. 3 shows that in order to reduce the muscular tension in the nerve system higher levels of illumination are required.

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Frequency of Blinking Vs Illumination

From figure 4 one can note that with increased illumination levels frequency of blinking is reduced. This is further corroborated by the convergence rate shown in Fig. 5

Convergence rate Vs Illumination Keeping this in view, Table I lists illumination levels for different Activities

Table I : Suggested Illumination Levels

Task Foot Candles Black thread on black cloth 800

News paper – stock equation 100 Typing on dark blue paper 80

Telephone directory 60 ( Yellow pages) News paper – text 40

Excellent printing 6 pt. 8 pt

10 8

Well formed letters 10 pt. 6 on pristine white background 12 pt. 5

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Visual criteria apart from illumination depends on Visual acuity, Visual efficiency, Visual speed and Visual health. Distinguish detail depending on brightness of the object, Characteristics of light entering the eye and Contrast details.

Fig. 6

Fig.6 shows the variation of visual acuity with background brightness. As may be noted 90% acuity levels are attained around 50 ft lamberts but increase to 95% requires 1300 ft lamberts.

Fig. 7

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Fig. 7 shows the acuity variation with surrounding brightness. The peak is seen to be around 1.2 – 1.4 ft L. It also shows that surrounding brightness should not be greater than object brightness. This is further confirmed by the data shown in Fig. 8.

Fig. 8

Fig. 9

Fig. 9 shows change in speed with increase in illumination levels. Curve A pertains to a white background. Over 1 to 40 ft lamberts, there is not much change in speed of reading. As opposed

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to this in case of Curve B pertaining to Gray background, increasing illumination improves the speed, very much.

Visual acuity reduces with age due to decrease in pupil size, decrease in elasticity of pupil and decrease in flexibility of optic lens and decrease in adjustment of local length leading to higher illumination requirement in older people. This may be seen in Fig.10

Fig. 10

Monochromatic light and acuity forms distinct images on retina and details are distinguished well. Gaseous source using Mercury and Sodium are used.Three primary colors are Red Green and Blue. Combination results in reduced acuity.

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Fig. 11 In Color Sensation of eye, Lag exists. Depends on presentation and cessation of stimulus, presentation of the object, rate of rise / fall of different colors. G – Green is slowest, B – Blue is fastest. Simultaneous Contrast is max. when adjustable e.g.: Red and Green. This lecture has looked into the functioning of the eye.Various quantities affecting the acuity. Lecture Summary

• Illumination affects physiology as well as psychology, hence quality lighting is important • Factors governing illumination quality :

• glare • diffusion • direction / focus • composition • distribution

• Minimum lighting required for good visibility is 100 ft-cd or more • For good visibility, brightness of surrounding should be greater than 0.01 ft-L & also

should be less than that of test object. • Apart from illumination, visibility is talked in terms of :

• visual acuity • visual efficacy • visual speed • visual health

• Acuity is the ability to distinguish details depending upon: • brightness of the object • characteristics of light entering the eye • contrast maintained

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• Age Vs. Vision

• reduction of visual activity • decrease in size & elasticity of pupil • decrease in flexibility of optic lens • leading to higher illumination requirement

• Monochromatic light & acuity : • distinct images on retina • details are distinguished well

• Combination of different colors reduces acuity which is known as Chromatic Aberration. • Color sensation by eye has a lag which depends on :

• presentation & cessation of stimulus • rate of rise / fall (different for various colors) • simultaneous colors & combination of colors

Tutorial Questions

• Why is quantity as well as quality of Illumination important?

At present eye tasks are more & for longer duration, hence increased illuminance is required. Illumination also affects psychology, hence quality is important.

• What should be the minimum brightness of the surrounding?

Brightness of surrounding must be less than that of the object and should not be less than0.01 ft-L

• What are the three primary colors?

They are Red, Green & Blue.

• How does aging leads to loss of vision?

Aging leads to decrease in adjustment capability of the focal length of eye. Thus higher illumination is required for older people

• What is chromatic aberration? Why does it occur?

It is the reduction in acuity due to combination of different colors. It occurs due to the fact that the eye lens has different refractive power for different wavelength of light.

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Module 1

Illumination Engineering Basics

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Lesson 5

Laws of Illumination Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

1. Define Standard of Illumination?

2. What is a Candela?

3. Understand MSLI

4. State Freschner’s Law

5. State Inverse Square law of Illumination. Laws of Illumination The original standard of light was Wax Candle, which is highly unreliable. It was replaced by a Vaporized Pentane Lamp. This is equal to10 original Candles. In the year 1909, Incandescent Lamp was taken as standard by comparison with a Pentane Lamp. Thing to be kept in mind is Primary Standard should be reproducible. It was in1948, Luminous Intensity; based on Luminance (objective brightness) of a small aperture due to Light from a Radiator maintained at 1773°c i.e. Solidification temperature of platinum was adopted as Standard. It consists of:

1. Radiator – Fused Thoria – Thorium Oxide. 45mm long internal dia of 2.5mm. Packed with Fused Thoria Powder at the bottom.

2. Supported Vertically Pure Platinum in a Fused thoria crucible with a small aperture of 1.5mm in a large refractory container.

3. Platinum melted by a High Frequency Eddy current.Luminance = 589000 Candles /m2 ≈ 600 000 units

The standard is shown in Fig.1.

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Transparent Common unit of light intensity is candela. It is Luminous intensity in the Perpendicular direction of a surface, 1 / 600,000 of a black body at temperature of solidification or Freezing of Platinum under Standard Atmospheric pressure. It is abbreviated as Cd. It is indicative of Light Radiating Capacity of a source of Lamp.

Fig. 2 Light flux Consider a transparent sphere of radius 1m shown in Fig.2. If we place a 1 Cd source at the centre then light flux coming out through an area of 1m2 over 1 steradian solid angle will be 1 lumen.

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Thus Luminous Intensity over 1 Str. by 1, Cd, we call it 1 lumen ≈ 1 lm. Basic unit of Light Flux. ∴ Total Flux = 4 π lumens, out of the sphere in Fig 2. If the Solid Angle be dω and Luminous Intensity I Cd at the center then Luminous flux in dω = dφ = I dω lm.

∴ dφI = Cd

Yet another important unit is MSLI. It means Mean Spherical Luminous Intensity. Average value of Luminous Intensity in all directions. Therefore for the case in Fig 2.

φ = I 4π lumens

Now we define Luminous intensity on a surface. It is known as Illuminance. It is Luminous Flux per unit area or lumens per sq m. = lumen / m2 = lm / m2 = lux (lx).

Fig. 3 Definition of Illuminance. Frechner’s law Weber in 1830 found that I – Stimulus (Intensity) produces dI – Least perceptible increment affecting sense organs. Then the ratio dI

Constant I= Under fixed – 1) Fatigue

2) Attention and 3) Expectation. Thus we have sensitivity given by the equation

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o

IS = C log (2)

I

Here I0 is the threshold intensity. This is known as Frechner’s Law. The same percentage change in stimulus Calculated from the least amount perceptible. Gives same change in sensation. Sensation produced by optic nerves have logarithmic dependence or relationship to Light Radiation producing the sensation. Inverse Square Law Intensity of Illumination produced by a point source varies inversely as square of the distance from the source. It is given by the equation and as shown in Fig. 3

2IE = (3)

D

Where I is Lambert’s Cosine Law of Incidence

2 I cosE = (4)D∝

This – tells us the variation of Illuminance on arbitrary surface inclined at an angle of α. As shown in Fig 4.

Fig. 4 Lambert’s Cosine Law of Emission I = I cos (5)∝ ∝

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Fig. 5 Typical Lighting Scheme Fig. 5 shows a lamp placed at A, bm above the floor. For this scheme Fig 6. shows the variation of Illuminance on the floor. It is well known that Illuminance is maximum under the lamp at ‘B’.

Fig. 6 Variation of Illuminance

2

LI in direction ABIlluminance at B =b

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2

LI in direction ACIlluminance at C =AC

2 2LI in direction AB× Cosθ=

(b d )+

2 2

LI in direction AB× b= 32(b d ) +

2 2

bCosθ = b + d

∴ Illuminance at C = Illuminance at Bx Cos3θ

32

Illuminance at B= 2d b( )[1+ ]

Next is to measure the candle power of the lamp. Typical measurement can be done using a photometric bench shown in Fig. 7 where IS represents standard lamp. IX represents test lamp. There is a screen at the centre called photometer head, adjusted for equal brightness on either side. Applying inverse law one can arrive at the value of IX. This lesson introduced the primary standard and other terminology related to measurement of light flux.

Fig. 7 Photometric Bench

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Lecture Summary

• Unit of luminous intensity is Candela (Cd), it is the luminous intensity of a surface which is1/600,000 of a blackbody, at the solidification temp. of Platinum (1773 °C) under standard atmospheric pressure.

• Luminous intensity over 1 steradian solid angle by a source of 1 Cd is called as 1 lumen flux (lm)

• MSLI = average intensity x solid angle (mean spherical Luminous intensity).

• Luminous Flux = luminous intensity × solid angle

• Illuminance is luminous flux per unit area

• Frechner’s Law – the same percentage change in stimulus calculated from the least amount perceptible gives the same change in sensation.

• Inverse Square Law – The intensity of illumination produced by a point source varies inversely as square of the distance from the source.

• Lambert’s Cosine Law of Incidence – 2

I×cosαE =D

• Lambert’s Cosine law of Emission – mI = I×cosα Tutorial Questions

• What is the standard unit of luminous intensity?

Candela (Cd)

• What is MSLI?

Mean Spherical Luminous Intensity. This unit is used as the light flux is radialy outwards from a source which may be assumed to be a point.

• What is the standard procedure to measure luminosity?

• Luminosity can be measured by the standard procedure of photometry

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Module 1

Illumination Engineering Basics

Version 2 EE IIT, Kharagpur 1

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Lesson 6

Photometry Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

• Understand photometric bench

• What is an Illumination Meter

• Understand Light Distribution Curves

• What is a Rousseau Diagram

• Understand a Luminaire. Photometry Primary Standard was defined in an earlier lecture based on the brightness of a body (i.e. black body) maintained at Freezing Temperature of platinum. Unit of Luminous Intensity abbreviated as is candela cd(z). Light Flux hence emanating from a point source in all directions is Illuminance - ¼ π lumens and is termed msli is the light flux incident on a task surface in lumens per unit area and is called lux. Comparison with a standard. Normally Primary standards are kept in standards Laboratories. Usually Incandescent Lamp Compared with a Primary standard is used as a Laboratory Standard. The test source / lamp is compared With the Laboratory Standard. However, Incandescent Lamp not suitable beyond 50 – 100 hours Standardization of Lamp is by voltage rating Current rating and wattage.

These measurements comprise photometry. They employ a Photometric Bench with a photometric head which is an opaque screen. These measurements involve compassing the test lamp with standard lamp

a. by varying the position of comparison lamp (standard Lamp) Is

b. by varying the position of the test lamp IT

c. by varying the position of the screen

Measurement is complete when the bench is balanced. It is balanced when two sides of the screen are equally bright [in a Dark Room] as shown in Fig. 1.

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Photometric Bench

2s

T s2 2I I = I = IS T S

⇒ 2T

Fig. 1 Photometric Bench Measurements may be made on Illumination meter or Lux meter also in this instead of the screen adjust the meter to get the same reading on photometric bench. Fig 2. shows a method where distance is varied to get the same reading on the meter.

Fig. 2 Use of Lux meter on Photometric Bench Alternatively, the distance on the bench may be kept constant and readings on the meter are noted.

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Fig. 3 Photometric Bench with Lux meter at a Constant Distance Then the intensity of the test Lamp is given by the relation

TReading with Test LampI = I × s Reading with Standard Lamp

………………………………………(i)

2

T s1

RI = IR

………………………………………………………………………(ii)

Fig. 4 Integrating Photometer

Fig 4 shows a typical photo meter. It has a standard point source ‘L’ of Light at the centre of a opaque sphere. It has an opening W where a photo cell is placed that receives diffused light from the source. Window ‘W’ is shielded by diffusing screen ‘C’ from direct light. Reading on the micrometer is first taken with a standard Lamp and later with the test Lamp. Then we have

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msli of test Lamp reading with test lamp=msli of standard Lamp reading with standard lamp ………………………… (iii)

from this, one can obtain light flux output of the test lamp by multiplying msli with 4π. Fig. 5 shows the photocell employed in a photometer. In a photocell sensitive element ‘S’ is selenium coated in the form of a thin layer on a steel plate P. This is in turn covered with a thin layer of Metal ‘M’ on which is a collection ring R.

Fig. 5 Photovoltaic cell Sensitive element is a semi-conductor that releases electrons upon exposure to light. Selenium and Cuprous oxide are most suitable semi-conductor materials. Steel Plate ‘P’ coated with thin layer of Selenium at 200°c and annealed at 80°c Producing crystalline form. It is in turn coated by a thin transparent film of metal ‘M’ with a collection ring ‘R’ of metal.

Fig. 6 Top view of a photo cell

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B is the barrier Layer Upon exposure to light – light enters through ‘M’ releases electrons from metallic Selenium. They cross barrier ‘B’ to ‘M’ and are collected through ‘R’ and P Current indicated by (A) is proportional to Illuminance. Often (A) is a micro ammeter calibrated in lm.

The next aspect of photometry is to look at the luminance curves of the Lamps. Here comes the role of Luminaries. Luminaries primarily provide the physical support to the Lamps. They may be directing, globes, reflecting or refracting. They could be supported on the walls using wall branects. They may be portable units on pole mounted in case of street Light. In all cares we need light distribution curves. Light distribution curves are curves giving Variation of Luminous intensity with angle of emission in a Horizontal plane i.e. Polar angle Azimuth or Vertical plane, passing though centre.

Fig 7 shows a typical Polar Luminance distribution curve of a point source of Light. From a Polar Curve in order to arrive at msli of the lamp a Rousseau diagram is constructed. Fig 8 shows such a construction.

Fig.7 A typical Polar Luminance distribution diagram

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Fig. 8 Rousseau Diagram Consider the Polar curve A for the typical lamp with O as centre of the Lamp Draw a semicircle of convenient radius OB = OC Insert no. of radii. From the top of there radial segments. From the tip of the radial segments draw horizontal lines extended to cut the vertical line to scale depending on length of Radic. Then the average width of the curve DP “Q” R “S” F is msli.

Luminaire They Provide Support and electrical connection to the lamp. They are used to control and direct the light and distribute as required. They help to keep the operating temperature within prescribed limits. Using Rousseau diagram, graphical techniques are employed to obtain the MSLI. They should be easy to install and maintain and have a pleasing appearance. They are expected to b economically viable. Thus Requirements for good luminaries may be listed as

i. to provide support & electrical connection to the lamp ii. to control, direct & distribute light as required

iii. to keep operating temp. within prescribed limits iv. should be easy to install & maintain v. should have aesthetically pleasing appearance and

vi. be economically viable In them Lens & prisms can be used for focusing the light one has to keep in mind Depreciation which is often used as Maintenance factor varies from 0.85 – 0.6. This lesson had a look at the ways of measuring light output of a Lamp. They consisted using photometric bench, either by comparison or reading on an illumination meter. Luminaries which form integral part of Illumination system are characterized by polar luminance curves. Way to assess their luminance has also been discussed.

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Lecture Summary Brightness is measured by a illumination meter which is a photoelectric cell comprising of a photo transistor activated by light. Brightness or luminance is the luminous intensity in the direction of interest per unit projected area

• Light output from a source of light is obtained by comparing it with a primary standard (standard lamp)

• Methods of comparing a test lamp with a standard lamp: • vary position of standard lamp • vary position of test lamp • vary position of the screen

• Luminnaires are used for directing the light from a source of light in the desired direction • Types of luminaires:

• directed reflectors • diffusing

Tutorial Questions

• Why can’t an incandescent lamp be used as a standard lamp? • What is utilization factor? • What is maintenance factor of a luminaire? • What are the advantages of diffusing type luminaire?

Answer to Questions of previous Lecture

• What is the standard unit of luminous intensity?

Candela (Cd)

• What is MSLI?

Mean Spherical Luminous Intensity. This unit is used as the light flux is radialy outwards from a source which may be assumed to be a point.

• What is the standard procedure to measure luminosity? • Luminosity can be measured by the standard procedure of photometry

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Module 2

Lamps Version 2 EE IIT, Kharagpur 1

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Lesson 7

Incandescent Lamps Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

• What are Incandescent Lamps?

• State the Components of an Incandescent Lamp.

• Understand need for inert Gas in Incandescent Lamp.

• What is Lamp Darkening?

• State Factors responsible for Performance of an Incandescent Lamps. Incandescent Lamps Natural Illumination due to sun which is 93 million miles away and 865,000 miles in dia, and has temperature > 6000°c, leads to 2.3 × 1027 cd. Luminance. Moon, 240,000 miles away and 2160 miles dia, is said to have I ≈ 1.0 × 1027 cd. In order to provide artificial Illumination one of the following Physical Properties is employed: Incandescence depending on thermo luminescence, Luminescence depending on electrical discharge in a gas or vapor Fluorescence depending on radiation of visible light by absorbing ultra violet light and Phosphorescence involving radiation at a latter point in time. Incandescent Lamps Incandescent Lamps were first invented by Edison in 1879. They employed Carbonized Paper as Filament. It was Fragile. Later it was improved by coating with a Hydrocarbon. In 1893 Cellulose Filament was developed from absorbent cotton dissolved in ZnCl. Normally Filament is mounted in a glass bulb and maintained in vacuum (type ‘B’) gets heated upon Passage of current and typically radiating 3.3 lm / W. They are called Type ‘B’ lamps. In 1905, Metallizing by heating Carbon filament at high temperature in an Electric furnace efficiency improved to 4.0 lm/W. In Europe Osmium a Rare & expensive – Fragile filaments were employed with 5 lm/W radiation. It was soon, replaced by Tantalum a Ductile material (1906 - 1913) by crystallizing by application of ac leading to 5 lm/W radiation. In 1907 Tungsten Filaments entered with 7 lm / W radiation. Finely divided Tungsten Powder is mixed with a binder and squirted through a die. In 1911 Coolidge developed Tungsten in ductile form which could result in a Continuous uniform Filament. It was Rugged and had very high efficiency. Langmuir introduced use of inert gases and improved the radiation efficiency – (1913). They ware called type ‘C’.

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Fig. 1 Incandescent Lamps Fig. 1 shows a typical Incandescent Lamp. It has filament made of Tungsten of S. G. 18.81 before drawing, 19.3 – 20.2 after drawing with a high mp of 3655°K. (Osmium with a mp of 2972°K & Tantalum with a mp of 3172°K). Were other materials Theoretically 52 lm / W radiation is possible at m.p but Practically, Highest radiation of 35.8 lm / W is achievable. They are available from 250W Flood Light with a life up 3 hours to 1500 W (at 115 V) of 1000 hr life radiating 22 lm / W. Smaller lamps being 6 W(at 115 V) with a 1500 hr life radiating 6 lm / W. Smallest Lamp being used in Surgical Instruments of 0.17 W of “Grain of wheat” radiation 0.35 lm. Largest Lamp being 50,000 W; 1,600,000 Lumens. Equivalent to 1000 - 100 W Lamps. Inert Gases are introduced in the Glass envelope to decrease the vaporizations of Tungsten. The gases Nitrogen and Argon are most suitable. Conduction Losses in a gas are proportional to velocity of gas molecules. Velocity is inversely proportional to square Root of atomic weight. Argon with atomic weight of 39.8 and Nitrogen with atomic weight 28.0 are most suitable. Ionization Potential of Argon is low. Hence a mixture of Argon and Nitrogen in the ratio of 85% Argon – 15% Nitrogen are employed. Concentrate the filament over a small region. To adopt tightly wound helical coil.

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Fig. 2 Blackening of Glass Bulb Fig. 2: shows darkening of Glass bulbs due to vaporization of Tungsten. Hence the lamps are called either Type B – Vacuum < 40 W rating or Type C – Gas > 40 W using Inert gases During operation Filament evaporates and Tungsten particles deposit on the interior of Bulb in a Vacuum Lamp. Tungsten Filament cross section of the Filament decides the current Rating and varies as square of dia. The radiation surface varies as dia. With decrease in operating voltage for the same wattage filament becomes larger. If a lamp of 40W were to operate at 115 V and has a cross section C 1S , it becomes C 2S at 220 V then C 1S > C 2S .

Fig. 3 Voltage vs Efficiency

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Fig. 3 shows variations of voltage with luminous efficiency for 40 W and 100W lamps. As may be observed for both the lamps variation in luminous efficacy between 200 – 240V is very little. It implies that small variations in voltage do not effect the light efficiency. Where as in the 110V region variation is significant though one gets higher efficacy compared to 220V region.

Fig. 4 Performance Curves

Fig. 5 Characteristics with change in voltage

Figures 4 and 5 show the performance of Incandescent Lamps. As may be seen from Fig. 4 both luminous efficacy lm/W and light flux lumeses reduce to 20% of Virgin values. Fig 5 shows the effect of variation of voltage from rated value. From this it may be said that although light output may reduce marginally when voltage reduces, one can get near 90% performance at about 95% rated voltage. Fig 6 shows the survival rate. More than 81% survive 80% stated life. Only 30% survive beyond 100% stated life.

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Fig. 6 Survival Rate

• Filament characteristics depend on Filament Length, Diameter, Coil Spacing, Lead wires, No. of Supports, Method of mounting, Properties of Gas, Gas Pressure, Bulb Size and Shape of the Bulb.

The lamp is said to be most economical for the intended Service, if uniform radiation is there at stated wattage with guaranteed efficiency and Life Rating. Lamp characteristics may be quantified interest of

Watts – W, Lumens – F, Lumens per watt – E, Life – L, and Volts – V

Equations (1) to (4) give the characteristics. They all show dependence on exponents a, b, c, d, e, f, g and h. Table I shows the typical values for Gas Lamps and Vacuum Lamp

( ) ( )a

1w v = VW

………

( ) ( ) ( )b cf v w = = 2 ?V WF

………

Typical cal values of Exponents

( ) ( ) ( )d eE v F = = 3V fe

……

( ) ( ) ( ) ( )f g hl V F E= = =v f eL

…… 4

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Table I: Typical Constants

a b c d e f g h

G

A 1.54 3.38 2.19 1.84 0.544 13.1 3.86 7.1

S

V

A

C 1.58 3.51 2.22 1.93 0.540 13.5 3.85 7.0

U

U

M

This lecture covered the characteristics of Incandescent Lamps. One important specifications of any light source is power consumed in watts. Any lamp is guaranteed to give radiation at stated efficiency, if operated around rated voltage.

Lecture Summary

• Incandescence – radiation at high temp. • Incandescent Lamps:

• Type-B : tungsten / osmium / tantalum filament, in vacuum • Type-C : tungsten filament, in inert gas (generally a mixture of Ar & N2)

• Tungsten is ductile in nature, has high MP & high efficiency which makes it suitable for use as filament

• Use of inert gas in incandescent lamps helps in decreasing the rate of evaporation of tungsten & improves efficiency

• Higher efficiency is obtained when incandescent lamps are operated at low voltages • Filament characteristics depend on

• filament length • filament diameter • coil spacing • lead wires • method of mounting • no. of supports • properties of gas employed • gas pressure • bulb size • shape of bulb

• Bulbs are designed for : • uniform radiation

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• accurate consumption of power • efficiency • life rating

Tutorial Questions

• What are the methods employed to tackle evaporation of tungsten filament in an incandescent bulb?

• use of inert gases in the bulb • adopt coiled filament.

• Why is it not feasible to operate bulbs at low voltages although it amounts to high efficiency?

With decrease in voltage current increases & it becomes difficult to handle large current

• What properties of tungsten make it a better material to be used as filament of a bulb?

High melting point, high efficiency, ready availability & ductility.

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Module 2

Lamps Version 2 EE IIT, Kharagpur 1

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Lesson 8

Discharge Lamps I Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

• What are Discharge Lamps?

• State Various type of Discharge Lamps

• List Types of Emission that make a Gas Conducting.

• Distinguish Line and Band Spectrum.

Discharge Lamps Incandescence was employed in Tungsten Filament lamps. Halides were employed to reduce blackening of the bulb. Lumniescence and Fluorescence increase efficiency far beyond incandescence. Discharge of electricity through a tube containing a conducting medium leading to electron Flow is employed in Lumniescence. This calls for an abundant supply of electrons. Electron Emission Electron emission is a process by which abundant supply of electrons is obtained. Electric Field Emission is employed in Cold cathode Lamps. Electrons are pulled out by application of High Potential. Thermionic Emission is employed in Hot cathode Lamps. Electrons are emitted even at a low voltage by heating. Barium / strontium oxide on a base of iron or Tungsten is used as Cathode. Photo electric Emission: Striking with Light Radiation of Photons, emission is achieved. Thus gas / vapor made Luminous by an electric discharge. Color / intensity of light are dependent on Gas / vapor employed. Intensity is proportional to the current. Commonly used gases are Neon, Mercury and Sodium. Cold Cathode needs large energy consumption at the cathode with decreased efficiency. This may lead to disintegration of cathode with high velocity positive ions due to large Potential drop at the cathode. Blackening of cathode does occur. They have Long Discharge Tubes with Low voltage Lamps. Mercury Vapor Lamps give light of Bluish Green, deficient in red rays. In this case color rendering (CRI) improves at high Pressures. Considerable distortion in colors occurs. Mercury – oxide coated Cathodes (Electrodes) are employed. In a typical discharge lamp coated tungsten wire electrodes with Strontium Oxide or Barium oxide coating are located at the opposite ends of a glass tube.

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Mercury Vapor Lamp

Arc is a Constant Current Phenomenon. The starting electrodes are connected to lower electrode through a resistance (R). Arc tube contains Mercury at the desired vapor pressure. Pure Argon initiates arc prior to vaporization as pressure is increased – Radiation moves into visible spectrum. Standard Rating are 100,250, ……3000 W with a typical illumination of 35 lm / W. Arc initiation takes place at 20V at about 5A. Argon arc lasts for 2 min with a bluish Glow. At about 137 V, 3.2 A – Mercury vaporizes and takes over. Run up time or arc initiation time is up to 30 minutes. Lowest run up time is around 2 minutes. Ballast is a reactor in series that limits the current. Typical Power factor ≈ 0.65 – 0.7 capacitors added across the Lamp improve power factor to 0.94.

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These lamps are suitable for Factory Lighting, Exterior Lighting / Flood Lighting and Street Lighting. They need 5 min of cooling before restarting. It is found that Combination Lamps – UV + Visible Light termed SUN Lamps with 3 min of Run up time and 5 min for restarting are more useful. They give out a band spectrum. Mercury – Radiates around 320 – 400 nm. Remember 365 nm is in the U.V. region. Sodium Vapor Lamp It is similar to High Pressure Mercury Vapor Lamp. It is in a hermetically sealed Glass tube with Sodium vapor. Electrodes are elliptical foil of Molybdenum and Coiled Barium oxide coated Tungsten. In one half cycle, Tungsten at the top acts as cathode, Molybdenum at the bottom acts as anode. Other Half cycle electrodes are reversed. Pure metallic sodium does not initiate arc. It needs a starting gas. Neon acts as a starter. This requires preheating, heaters are provided with in the Lamp. The Lamp glows with Red Color (Neon vapor), Orange yellow arc (sodium vapor arc). Leads to a line spectrum of radiation.

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Figs. 3 to 7 show the Radiation spectrum for various sources along with curves for human eye sensitivity. In each curve the hatched region indicates, theoretically possible radiation energy in the visible region. It may be observed that incandescent lamp has maximum energy in the visible range and has a continuous spectrum. Lecture Summary

• Luminescence – chemical / electrical action on gas / vapor producing radiation • Fluorescence – radiation is absorbed at one wavelength & radiated at another wavelength • Combination of luminescence & fluorescence increase efficiency far beyond

incandescence. • Discharge lamps consist of discharge of electricity through a tube containing a

conducting medium • Types of electron emission

• Electric Field Emission • Thermionic Emission • Photoelectric Emission

• In a discharge lamp : • gas / vapor made luminous by an electric discharge • color / intensity are dependent on gas / vapor used • intensity to some extent proportional to current.

• Types of discharge lamps : • Mercury Vapor Lamps.

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• Sodium Vapor Lamps • Hg-lamps give a light bluish green color (deficient in red color) • In a Hg-vapor lamp, a starting electrode is provided to initiate the arc. After a run-up time

of 2 min., Hg-vapor discharge starts. • Gas at high pressure improves the CRI (color rendering index) of discharge lamps • With Na-lamps a pre-heating heater is provided. The lamp glows initially with red color

(Ne-vapor discharge) & then turns to orange yellow arc (Na-vapor discharge) Tutorial Questions

• What are the different electron emission methods? What method is employed for Hg-vapor & Na-vapor lamp?

The different methods are electric field emission, thermionic emission & photoelectric emission. In Hg-vapor lamp electric field emission & Na-vapor lamp thermionic emission

• What are the commonly used gases in discharge lamps?

Commonly used gases are Sodium, Mercury, Neon & Argon

• What are the disadvantages of using cold cathode lamps?

Cold cathode lamps consume large energy consumption at cathode and therefore decreased efficiency. Also it often results in disintegration of cathode.

• What do you mean by run-up time?

The taken by the starting gases (Ne / Ar) in the discharge lamp to initiate the discharge process of the main gas (Na / Hg).

• Why do we connect a choke / ballast in series with a Hg-vapor lamp?

It enables high potential build up at the cathode while starting & limits the current thereafter

• What steps are taken to improve the low power factor of a Hg-vapor lamp?

Generally Hg-vapor lamps have low power factor. To improve the power factor capacitors are connected in parallel with the lamp

• What do you mean by principle line? What is the principle line for Hg-vapor lamp?

It is the wavelength on the lamp output spectrum which gives the maximum light output. For Hg-vapor lamp it is 365nm

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Module 2

Lamps Version 2 EE IIT, Kharagpur 1

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Lesson 9

Discharge Lamp II Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

1. List various Discharge Lamps.

2. State Utilization Factor for a Discharge Lamp.

3. What is color rendering.

4. Understand Working of a Fluorescent Lamp.

5. State various types of Phosphors usable.

Discharge Lamps (contd)… As already seen in the last lesson Sodium Vapor Lamps are placed most favorable from the utilization point of view with high utilization factor. Low Pressure Mercury Vapor Lamp is seen to radiate clear blue line Spectrum. Low Pressure Sodium vapor radiates Monochrome light. High Pressure Mercury vapor with certain additives like Halides can be made to radiate multi line spectrum. Low Pressure Mercury vapor utilizes only 25 % of energy as compared to Incandescent Lamp. Consuming 7-11 W, with a burning for 5000 hrs. Normally fluorescent lamps based on low pressure mercury vapor are recommended for Homes, Hotels and Restaurants. They give warm white color and are often used as Blended Lamps. Low Pressure Sodium Lamp with outer Envelope’s inner surface coated with Indium oxide as selective IR reflector. They have efficacy up to 200 lm / w and are available from 18 to 180W. They are suitable for lighting Highways, Harbors, Marshalling Yards etc. High Pressure Mercury Vapor Lamp are available in the range of 50w to 2000w. The radiation obtained is Bluish white line spectrum. Pure Mercury vapor lamps have very poor CRI, together with phosphors color improves, very much. Halide-iodide additives of Indium and Thallium or Sodium are added to reduce blackening of bulb. High Pressure Sodium Vapor Lamp have excess of sodium which saturates as Vapor of Sodium. Mercury and Xenon are used as buffer gases for ignition. These lamps operate around 700ºC with a color temperature of 2100° k at 130 lm / w efficacy.

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Table I Properties of Discharge Lamps MERCURY SODIUM PROPERTY INCANDESCENT

LP HP LP HP Flux lm 250 - 40000 450-1200 2000-

125000 1800-33000

3300-130000

Efficacy lm / w 10 - 20 41-50 40-63 100-183 70-130 Rating w 25 – 2000 9-25 50-2000 18-180 50-1000 Light Color Warm-white warm-

white intermedi

ate warm-white

warm-white

Color rendering Excellent Good Moderate non existent

Poor

Ballast None built-in Chock hybrid Choke Starter

None

Built-in

None

Separate or Built into

Ballast

Run up time min

Zero Zero 3 10 5

Restrike time min

Zero Zero 5 2 <1

Table I lists various properties associated with various types of discharge lamps. Fluorescent Lamp

Employs transformation of UV radiation due to low pressure mercury vapor. Luminescent Powder in tubular vapor Lamps Enhances brilliancy of light. Radiation from Low Pressure Mercury Vapor (which is in UV region) is impinged on Luminescent Materials and re – radiated at longer wavelengths of visible spectrum. In a Glass Tube small drop of Mercury and small amount of Argon gas are placed for initiation of discharge. Pressure, voltage and current are so adjusted that 253.7 nm line is excited. This re-radiates at longer wavelength. Typically a 40W lamp requires 2-3g of phosphors. Maximum sensitivity is around 250 – 260 nm. Various types of Fluorescent Lamps are:

1. Day Light Fluorescent Lamps - Average Noon Day Light. 6500°k suitable where demands are not exacting 2. Standard white Light - 3500°k general Lighting. 3. 4500°k white Lamp – between std. white Light & Day Light Lamp. 4. Soft white Lamp – Pinker Light. 25% lower light output than Std. white Lamp suitable

for Residential lighting and Restaurants. Dimension and Voltage depend on Luminous Efficacy, Brightness, Lumen Output and Lumen Maintenance. Reliable Starting is achieved by having preheated cathodes / hot cathode. Half the open circuit voltage should be used by the Lamp and the other half by the ballast. Lamp Voltage decides the arc length, bulb diameter and lamp current. Hot Cathode lamps operate at lower voltage < cold Cathode lamps. Typically cold cathodes have 70-100V drop at the cathode.

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Figure1 shows the schematic of a typical Fluorescent lamp. In a normal lamp the ratio of open circuit voltage to lamp voltage drop is 2 where as in an instant start lamp it is around 4. Figure2 shows the radiation sensitivity of various phosphors. As may be observed, the peak sensitivity at 253.7 nm is for Zinc Beryllium Sulphate. Table 2 lists various phosphor properties. For each material emitted color after fluorescence, range of emission, peak emission wavelength and peak sensitivity are listed. It may be observed that Zinc Beryllium Silicate has peak emission coinciding with peak eye sensitivity. Hence this is the most commonly employed phosphor.

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Table 2 Characteristics of Fluorescent Chemicals

Phosphors Color Exciting Rang nm

Sensitivity Peak nm

Emitted Range nm

Emitted Peak nm

Calcium Tungstate

Blue 220-300 272 310-700 440

Magnesium Tungstate

Blue – white

220-320 285 360-720 480

Zinc. SiliCate Green 220-296 253.7 460-640 525 Zinc Beryllium silicate

Yellow white

220-300 253.7 480-750 595

Cadmium Silicate Yellow Pink

220-300 240 480-740 595

Cadmium Borate Pink 220-360 250 520-750 615

Lecture Summary

• LP Na-vapor Lamp – in this type of lamp the outer envelope of inner surface is coated with Indium Oxide & that acts as an IR – reflector

• HP Hg-vapor Lamp – gives rise to bluish white line spectrum, together with some phosphors improves color If some luminescent powder • light Radia

is put in the tubular lamps it enhances brilliancy of

• tion from LP Hg-vapor lamp (which is in the UV-region) is impinged on

• Factors deciding the dimension of fluorescent lamps : y

ting • Factors deciding the lamp voltage :

luminescent materials to reradiate at longer wavelength of visible spectrum Types of Fluorescent Lamps :

• Day Light Lamp p • Standard White Lam

• Soft White Lamp

• luminous efficienc• brightness

lumen output • • lumen maintenance • reliable star

• arc length • bulb diameter • lamp current

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Tutorial

• What are halide lamps?

These discharge lamps contain some additives like Indium, Thallium

• Why are Hg-vapor lamps preferred than Na-lamps?

Hg-vapor lamps have a good CRI while Na-vapor lamps are monochrome

• Describe the working principle of a fluorescent lamp.

The energy of the UV radiation from a LP Hg-vapor lamp is directed on luminescent materials. These in turn give out radiations in the visible region.

• For what wavelength do we get maximum efficiency for a fluorescent lamp?

Maximum sensitivity is achieved at 253.7 nm

• How do we obtain reliable starting of a fluorescent lamp?

By having preheated cathodes or hot cathodes

• What are the voltage drop at the electrodes & the choke for a fluorescent lamp?

At the choke the voltage drop is half the operating voltage. If the cathode is a hot electrode type then voltage drop is 14 – 16 V and if it is a cold cathode type then voltage drop is 70 – 100 V.

Questions

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Module 2

Lamps Version 2 EE IIT, Kharagpur 1

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Lesson 10

Discharge Lamp III Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

1. How are Fluorescent Lamps specified.

2. Understand how every watt of Power is spent in a fluorescent lamp.

3. State Various applications of UV Light

4. What are CFLs?

5. How do CFLs compare with Ordinary Lamps? Discharge Lamps (contd.) Continuing with our discussion on Fluorescent lamps, for a given Current & tube diameter, Voltage Increases as length increases, Voltage Decreases as Diameter increases and Voltage Decreases as Current increases. In other words the ratio of length to diameter remains a constant. Inherently brightness is more at the ends. It is low 6-7 diameters from the end. They are specified as Tx, where x denotes that diameter and is x/8 inches. Typically Hot Cathode lamps have 14-16V voltage drop at Cathode, while Cold cathode lamps have 70-100V drop at cathode. Further, radiation increases with the current density. At low temperatures, pressure drops and Mercury tends to condense. To avoid prefer to operate at high temperatures. Bulb Temperature Vs Light output

Fig 1 shows the variation of light output with bulb temperature. Shaded region indicates normal operation at room temperature. It is seen to have a peak around 100º F. Fig 2 shows the relative efficiency of a 1.5” dia lamp (≈ T12) lamp, with tub length. As may be seen about 80” – 100” are necessary to get a reasonably good light output.

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Having understood functioning and characteristic of a fluorescent lamp, it is time, we looked at the energy distribution. Relative Efficiency of 1.5” Diameter Lamp

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As may be seen from Fig 3, which shows the energy distribution of a typical 40 W Fluorescent Lamp, about 20.30% results in useful light output. About 26% is radiated as heat and 53 % results in conductive and convective heat. Important observation to be made is that about 18% light output is through fluorescence. This is the reason; we say that they are more efficient than incandescent lamps.

UV radiation apart from being used to illuminate employing fluorescence is also used for Purification, Detoxifying Bacteria, Curing of Rickets, Colds, TB, and Pernicious Anemia.

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Ultraviolet radiation is beneficial in small quantities but direct exposure to heart kidneys should always be avoided. In industry it is used for production of Dyes and Food Preservation. UV radiation helps in producing Vitamin ‘D’ in Food Sources in Plants and Animals. Various peak sensitivities for different applications are:

1. Germicidal – 260 nm Peak.

2. Erythemial – 296 nm Peak.

3. Fluorescent / Black light – 253.7 nm Peak.

Figs. 5, 6, 7 show typical characteristics of the fluorescent lamps. From Fig 5 it is quite clear that mere increase of current does not guarantee increase in light output.

Fig 6 tells us that one can expect about 2000hr of life with about 80% of nominal output light.

Mortality curve in Fig 7 tells us that close to 80% lamps have more than 80% nominal life. This helps us in arriving at a clear lamp replacement policy.

Fig 8 shows a typical CFL or Compact Fluorescent lamp which is compact with all accessories, with fixture so arranged as to fit in an outlet meant for an incandescent lamp.

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Lumen Maintenance Curve

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Fluorescent Lamp Mortality Curve

Table 1 compares the characteristics of various fluorescent lamps.

Table 1: Properties of Fluorescent Lamps

Conventional Energy Saving CFL 150-5300 lm 600-4800 lm 38-91 lm/W 4-65W 24-28W 9-55W Warm white color - 54W Excellent Color Rendering Good CR Good CR

Choke additional Inbuilt Inbuilt Zero Run up time Zero Restrike time 5000 hrs. 18000 Hrs 8000 hr Rs.400/- Rs. 1000/- Rs. 40/- 20 mm 38 mm, 28-26 mm

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In addition there are RS or rapid start lamps where electrodes are continuously heated. For instant start, preheated cathodes with reasonably high starting voltage are used. In Explosive environments lamp caps thick with long pins having maximum surface contact are used to avoid sparks. This lesson has had a look at the characteristics of fluorescent lamps. Lecture Summary

• Fluorescent lamps are LP Hg-vapor lamps • For a given current & tube diameter of fluorescent lamp we have :

• voltage is directly proportional to length • voltage is inversely proportional to diameter • voltage is inversely proportional to current through discharge tube

• By a T12 fluorescent tube we mean that a tube with diameter of 12 × (1/8)” = 1.5“ • Radiation output from a fluorescent tube is directly proportional to the current density in

the tube. • Fluorescent lamps emit a considerable amount of UV & IR radiation along with visible

radiation • UV radiations is beneficial in small quantities. Applications of UV radiation:

• purification • detoxifying bacteria • curing of diseases • dye & food processing • employed in producing Vitamin-D in food sources

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• Compact Fluorescent Lamps (CFL) are compact, efficient, energy saving, higher lifetime, reasonably good CRI & near daylight illumination characteristics. Moreover they have all the accessories inbuilt. Hence they are better than common fluorescent lamps

Tutorial Questions

• What do you mean by a T16 tube light? By a T16 fluorescent tube we mean that a tube with diameter of 16 × (1/8)′ ′ = 2′′

• Why is hot cathode discharge tube preferred than cold cathode discharge tube?

Hot cathode has a voltage drop of 14-16 V whereas cold cathode has a voltage drop of 70-100 V. hence to avoid large voltage drop hot cathode is preferred

• Why is it desirable to operate fluorescent tubes at room temp.?

At low temp., pressure drops & Hg tends to condense while it is unsafe to operate at extreme high temp. Hence fluorescent tubes are operated at around room temp.

• What are three categories of usage of UV radiation? • Germicidal • Erythemal • Fluorescent / Black Light

• What are rapid start & instant start fluorescent lamps? • in rapid start, filaments are heated continuously • in instant start, preheated cathode is present

• What precautions are taken to use fluorescent lamps in explosive environments?

Lamp caps are present and long thick pins are used to offer maximum surface contacts thereby avoiding sparks

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Module 3

Illumination Systems Version 2 EE IIT, Kharagpur 1

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Lesson 11

Illumination Systems I Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

1. List Components of an Illumination System.

2. What is a Luminnaire?

3. What are various forms of Lighting? Illumination Systems It is time we looked at an illumination system as a whole. These systems tend to produce radiation close to natural radiation. They employ artificial sources. These sources obey Laws of Illumination. The quantification is done through Photometry. Thus an Illumination system consists of Lamp which may be Incandescent lamp, Discharge lamp or Fluorescent lamp along with control gear placed in a suitable luminaire. Luminaries Luminaire or Luminaries provide support and electrical connection to Lamp or Lamps within it. They control, distribute and direct the Light on to the object. They ensure that lamps are operated in a way such that operating temperature is kept within prescribed limits. They should be easy to install and maintain, aesthetically pleasant and economically viable. Systems may be commercial or general. Usually Fluorescent Lamps with one or more at a preferred mounting height less than 5 – 6 m are used for general lamps. Fluorescent Lamp may be Batten Fully exposed or Multi lamp type. Ventilated-Reflectors with Mirrors optics are used. Difference lies in control of Luminous Intensity, Luminous distribution, No. of Lamps. One may recall that for a

Point source of radiation 2

1d

∝ (e.g one can recall that Incandescent Lamp),

Line source of radiation 1d

∝ (e.g. Tube Lights), and

Plane Source of Radiation ∝ independent of distance (Ideal situation). Here‘d’ is the distance to the source of light. Designer aims in locating Lamps in this fashion. Reflectors help in controlling and directing the light. Louvres-opening with slanted Slates are often employed. Fins / vanes are provided to ventilate. Batten mounted lamps amounts to no control. Most systems have enameled reflectors. Improved ones have Mirror reflectors. Additional control obtained through louvre shields and opalescent shades. Reflectors help direct in a desired solid angle. Louvres may have Square Mesh Box type Luminaries or Diamond Mesh or Lamellae -Thin Plate Layer type.

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Fig 1 shows a typical luminaire with reflector and louver. The luminaries may be recessed in the ceiling, mounted on the walls (or a surface) or take box shape as shown in Fig 2. They are suspended at times.

Efficiency of Luminaries is expressed in terms of Light Output Ratio ‘LOR’

LOR = light output with luminaries individual light output(w/o luminaries)Σ

This includes both downward as well as upward light. Down ward light is important from the utilization point of view. Hence, DLOR is crucial. Up ward light illuminates indirectly by reflection. With Mirror Reflectors, LOR goes up and Glare comes into Consideration. Industrial Luminaries Coming to industrial areas if in the Interior-up to 6m Fluorescent Lamp with matt white reflector are employed. In High bays beyond 6m Discharge Lamps with Mirror Reflectors are employed. Luminaries in Hazardous Areas are specially deigned. They are encapsulated in boxes made of steel or cast iron exterior housing to avoid any explosion, sturdy resisting pressure. Categories of Explosive Areas In this respect explosives are as are categorized as

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Zone 0 – Explosive all the time, Zone 1 – Normally Explosive and Zone 2 – Explosive Abnormally. Here moisture & dust are taken care by Gasketted Luminnaires – Completely sealed eg: in a Shower or a Laundry. Emergency Lighting is required when normal lighting fails. Escape Lighting sufficient for evacuation typically 1 – 10 lx. Safety Lighting – � 5% normal Lighting is provided in Potentially Hazardous areas. Stand by power supply required for activation of vital implements. A permanent, separate, self supporting Power system which is reliable and mains rechargeable batteries in each Luminnaire are provided Non Permanent - Auto Switching - Emergency Generator - Battery Supply is also used. Road Lighting Conventionally by they are arranged in a column, mounted on a wall or suspended by a span wire. Plane of Symmetry being in vertical plane perpendicular to the axis of the road along the road. Catenary – suspended from a catenary cable parallel to the axis of road. Plane of symmetry parallel to the axis of road. They employ Corrosion Resistant sturdy materials and are usually closed.

Flood Lights Rain Proof Lamp holder with wide / narrow beam Reflectors are used for flood light. They are usually High wattage Incandescent Lamps, Halogen Lamps, High Pressure Mercury Vapor Lamp or Low / high Pressure Sodium Lamp. Spot lights / down lights are usually used with Screens, Reflectors, Filters, Colored envelope and Closed Lamps. Down lights are Spot lights when suspended. This lesson has had a look at the components of an Illumination system under various scenarios.

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Lecture Summary

• Illumination system comprises of a lamp (the artificial source of light), luminnaires & the control gear

• Commercial luminnaires can be categorized into • General • Industrial

• Luminnaires are characterized by the way they control & direct light : • luminous intensity • luminous distribution • number of lamps

• Use of mirrors in luminnaires are avoided as they cause glare • Efficiency of a luminnaire is talked in terms of light output ratio (LOR). This includes

both downward as well as upward light. • Practically DLOR (downward LOR) is of importance • Luminnaires for hazardous areas :

• maintains temp. • is encapsulated to resist pressure

• Gasketted luminnaires which are completely sealed takes care of handling moisture & dust.

• Emergency lighting should have self supporting power system to provide lighting when normal lighting fails

Tutorial Questions

• Which type of lighting are used for general lighting & why?

Incandescent & fluorescent lamps are preferred because they have a good CRI & provide near day light illuminance

• What are louvers?

They are opening with slanted slates often used with luminaires to control & direct light

• What are the different luminaires considered placement wise? • box type, • recessed in the ceiling, • mounted on a surface and • suspended from a ceiling

• What type of lighting is used in industrial lighting?

For interior lighting fluorescent lamps with matt white reflectors are used while for high bays discharge lamps with mirror reflectors are used

• What are the different types of emergency lighting used? • Escape lighting – just sufficient lighting, • Safety lighting – not less than 5% of normal lighting, • Standby lighting – for activation of vital implements when power fails

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Module 3

Illumination Systems Version 2 EE IIT, Kharagpur 1

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Lesson 12

Illumination Systems II Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

1. Understand the accessories employed in Illuminating systems.

2. What is a Ballast?

3. List various types of Ballasts.

4. List starting devices. As already brought out the components of an Illumination system are Lamp, the Radiation Source, Luminaire that directs and controls the light flux. Control Gear is the accessory that helps in controlling the requisite amount of flux on the work plane. Now we take a look at the accessories involved. First of these is Ballast. In a discharge lamp a series impedance to limit the current is required. If the current is allowed to increase there can be explosion of the lamp. This takes the form in a.c. as Inductance-w/o undue loss of power. This is called Ballast. It should have high power factor for economic use of the supply and should generate minimum harmonics. It should offer high impedance to audio frequencies.It should suppress-Electromagnetic interference (Radio interference-TV interference). It is essentially, a reactor of a wound coil on a magnetic core often called Choke and is in series with the lamp. Typical power factor is 0.5 Lag. Power factor is improved by having a capacitor connected across input lines.

Fig 1 shows the connection for a discharge lamp employing a ballast formed by a reactor commonly known as choke. Fig 2 shows how the capacitor may be connected to improve the power factor. As may be seen the capacitor is placed in shunt. At times a lead circuit may result by placing a capacitor in series as shown in Fig 3. However, when a illumination system employing two lamps is used power factor may be improved by having one with a lead circuit and other with a lag circuit as shown in Fig. 4. Next important accessory is a starter that initiates the discharge in a discharge lamp. Starter is marked as ‘S’ in the Figs.1 to 4. Starter less circuit are shown in Fig 5. They employ pre-heated filament electrodes. The preheating obtained through a small portion of voltage tapped from the input source.

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When discharge lamps are used on dc the ballast takes the form of a resistor together with associated power loss. These days they take the form of an electronic ballast which converts dc to high frequency ac of around 20 kHZ.

Except high pressure mercury lamp where V > VS (starting) all lamps need a starting device. At times, it is integral part of a lamp. Switch start employs bimetallic strip that opens upon

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heating. Starterless, rapid start or instant starts are useful for outdoor applications. Other forms of starters employed are three electrode devices called ignitors.

Ignitors are small 3 electrode devices, which are ignited by control pulses from small electronic circuit. Typically Metal Halide lamps require 600 – 700V and Low Pressure Sodium Vapor lamps require 400- 600V. Ignition is through a Thyristor that generate a set of HV pulses, which

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are stopped after Lamp glows or ignited. High Pressure Sodium Vapor Lamp needs about 3000V. Different Light Flux Levels are required at different times. This consists Local and General Lighting taken care by having dimmers and lamps of different wattages. Fig. 7 shows a typical Dimmer stat.

A dimmer stat is an autotransformer that can give a variable output voltage. Fig. 8 shows a typical metal halide lamp employing ignitor as a starting device. Fig. 9 shows a typical scheme for a multi watt circuit. Typically street lighting requires such multi watt lamps. High wattage lighting is employed during heavy traffic and low wattage during the rest of the night. This lecture thus covered the accessories necessary in an Illumination system.

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Lecture Summary

• Control gears are the accessories that help in controlling the requisite amount of light flux on the work plane

• Gas discharge lamps are constant current devices. Constant current is achieved by use of ballasts.

Requirements for good ballasts:

• less undue power loss • should offer high impedance to audio frequency • should suppress EMI / RFI / TVI • should provide proper starting conditions • should have as high power factor as possible

To improve power factor capacitors are used in series.

• Excepting HP Hg-vapor lamps, all lamps have starting voltage > spark over voltage. Hence starters & igniters are used as starting devices.

• Igniters are small three electrode devices which are fired by controlled pulses from small electronic circuits.

• Apart from local & general lighting dimmers / timers are used for two – stage lighting Tutorial Questions

• Why are inductors preferred for use as ballasts? They provide high starting voltages without undue loss of power.

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• What is the disadvantage of using inductance as ballasts? How can it be rectified? Inductance have low power factor which is undesirable. Hence series capacitor or lead-lag circuits are used for improving the power factor

• How can we stabilize current when a DC source is used? What are its disadvantages?

Resistance are used to stabilize current but they have a constant power loss

• What is the principle of operation of starterless circuits? What is its usefulness?

They work on the principle of semi-resonant circuits. They employ preheated filament electrodes which draw small amount of voltage. They are useful in smooth operation of discharge lamps at extreme cold conditions

• What are switch type starters?

They are bimetallic switches which remain close while starting & opens upon heating when lamp glows

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Module 3

Illumination Systems Version 2 EE IIT, Kharagpur 1

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Lesson 13

Glare Version 2 EE IIT, Kharagpur 2

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Instructional objectives

1. Define Glare.

2. List types of Glare.

3. List the effects of Glare.

4. What are various Glare Indices

5. How is Glare Evaluated?

6. List measures to reduce the Glare.

An important issue in effective use of an illumination system is Glare. Glare by definition brightness within the field of vision that causes discomfort, annoyance interference and eye fatigue. It reduces the visibility of an object. This is the common fault of lighting installations. It injures the eye, disturbs the nervous system, causes discomfort and fatigue, reduces efficiency, interferes with clear vision and increases risk of accident.

Glare is experienced, when Lamps, Windows, Luminaries, other areas are brighter than general brightness in the environment. Glare may be Direct and Reflected. Direct glare results from bright luminaire in the field of vision. Reflected glare arises due to reflection of such a source from a glossy surface it is more annoying than direct glare can be avoided by appropriate choice of interiors.

Direct glare, minimization or avoidance is possible by mounting luminaries well above the line of vision or field of vision. Limit both brightness and light flux (in the normal field of view). Disability glare is that level of glare that impairs the vision. Whereas Discomfort glare only causes feeling of discomfort that increases or depends on time of exposure. There is no reduction of visual acuity but leads to fatigue. Annoyance is at lower ever luminance of the glare but source is more than the general luminance. Solid angle subtended at the observer’s eye in the field of view is a measure of glare. There is a need to look at the Glare Evaluation System. Glare Evaluation Visual comfort system is most common evaluation in the USA/Canada. This is expressed as percentage of people considering an installation comfortable as viewed from one end. Glare tables list various proportions and layout of room for glare free lighting. Figure of merit is based on a source of 1000 lm.from a luminaire. If VCP ≈ 70% then the system is said to be glare free. British method employs Zone of luminaire with a classification for quality of light expressed as Glare index. Luminance limit system is adopted in Australia. Standard code for Luminaire base lamp. dep. on room dimensions, mounting height and a Empirical shielding angle

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Luminance curve system is employed in Europe. Luminance limits for luminaires critical angles, γ are 45º < γ < 85º. Quality class is expressed from A to E type is based on Luminaire orientation. Type 1. Luminous sides when Luminous side plane> 30 mm

Type 2. Elongated - length > 2width

Orientation C0 – C180 Plane

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Table I

Shielding Angle Glare Limit Lamp Luminance Cd/m2 B D E Fluorescent lamp. L ≤ 2.104 10º 0 0 HP discharge lamp 2.104 < L ≤ 50.104 15º 5º 0º LP Sodium lamp L > 50.104 30º 15º 0º HP Discharge clear

Table I lists for different types of lamps effective shielding angle. Quality class A denotes very high level; B denotes high, C medium D low and E very low. General light is predominantly light coming downwards. Typically reflectance of 0.5 for walls / ceiling and 0.25 for furniture.

How is Glare evaluated?

1. Determine luminance of the source between 45º - 85º 2. Determine the quality class and illuminance required. 3. Select the curve – class / level. 4. Determine. Max. Angle to be considered from length & height and plane of eye level &

plane of luminaires. (Refer to Fig 1) 5. Horizontal limit based on” a / h”, part of the line ( or curve) to be ignored. 6. Compare luminance of one luminaire with selected part of the limiting curve.

No glare if luminance given by the curve > actual luminance over the whole range of Emission.

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Table II

Quality class

Service values of Illuminance (lux) Glare rating

A 2000 1000 500 ≤300 1.15 B 2000 1000 500 ≤300 1.50 C 2000 1000 500 ≤300 1.85 E 2000 1000 500 ≤300 2.20

Luminance curve system

F 2000 1000 500 ≤300 2.55 Curve

letter a b c d e f g h

British Glare Index

15,5 17,0 18,5 20,0 21,5 23,0 24,5 26,0

American VCP 75% 65% 45% Table II lists glare in dicer and curves to be used for different levels of illuminance and quality.

Quality class

G

Service values of Illuminance (lux)

A 1.15 2000 1000 500 ≤300 B 1.50 2000 1000 500 ≤300 C 1.85 2000 1000 500 ≤300 E 2.20 2000 1000 500 ≤300 F 2.55 2000 1000 500 ≤300

a b c d e f g h

Fig 4 and 5 show the luminaire curves to be employed for different levels for Type I luminaire and Type II luminaire.

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h IllumA (B) IllumD IllumC

1 1.35 I/h2 1.425 1.43 I/h2 2 1.72 I/h2 1.798 1.827 I/h2 3 1.85 I/h2 1.902 1.919 I/h2 4 1.91 I/h2 1.943 1.95 I/h2

Illuminance at A (B) = 3

2 2

1 h1+

h h +1

⎡ ⎤⎛⎢ ⎜⎢ ⎥⎝ ⎠⎣ ⎦

⎞⎥⎟ (i)

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Namely height is an issue in avoiding glare. Fig. 6 shows two lamps placed at a height ‘h’ from ground at A and B. As can be seen from relations (i), (ii),(iii). Illuminance below the lamp falls rapidly, less rapidly at the mid point ‘C’.

Illuminance at C = 3

2 2

1 h *2h h + 0.25

⎡ ⎤⎛ ⎞⎢⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

⎥ (ii)

Illuminance at D = 3 3

2 2 2 2 2

h h1h h + (0.75) h + (0.25)

⎡ ⎤⎛ ⎞ ⎛⎢ ⎥+⎜ ⎟ ⎜⎢ ⎥⎝ ⎠ ⎝⎣ ⎦

⎞⎟⎠

(iii)

h ↑ (i) ↓↓↓ (ii) ↓↓ (iii) ↓

Glare from windows is the next issue. Sky has a typical luminance of 2000 Cd/m2. Horizontal Illuminance ≈ 10,000 lx. under overcast conditions. It is prevented by curtains, blinds, louvers. Opening of windows can be reduced. Shift the work plane away from offending windows. i.e. normal field of view no light enters from the offending window on the work plane. Lightest decorative finish on surfaces surrounding window openings. Veiling reflections and reflected glare are allowed outside the task. Reflected by glossy surface – semi matt. Mild distraction can cause considerable discomfort. When glare (bright light) on the task. Veiling reflection – reduce task contrast with some loss of details. Glare can be minimized by not locating in the forbidden zone, increase light from sideways at right angles to the direction of viewing. Luminaries having large surface area with low luminance may be employed. Working surface to be provided with reduced reflection preferably Matt surface CRF (Contrast Rendition Factor) is yet another index and influence of Lighting on Task Contrast and Task Visibility is Contrast Rendition Factor. By definition

Task visibility = Given EmmisionSphere Illuminance

Where Sphere Illuminance is the Illuminance by the source providing equal Luminous Intensity in all directional in a hypothetical sphere. (ESI) Observer is located / views at angle of 25º to the vertical. Observer considered to be viewing pencil task which id believed to be slightly conveying.

This lecture has had a look at glare, how originated various evaluation procedures and ways to minimize.

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Lecture Summary

• Glare is the brightness within the field of vision • Effects of glare :

• injures the eye • disturbs the nervous system • causes annoyance, discomfort & fatigue • reduces efficiency of work • interferes with clear vision • risk of accident increases

• Types of glare : • Direct Glare • bright luminaire in the field of vision • Reflected Glare • reflection from a glossy surface

• Reflected glare causes more annoyance than direct glare • Direct glare can be minimized by mounting luminaires well above the line of vision • Disability Glare impairs the vision • Discomfort Glare increases with time of exposure • Glare Evaluation Systems :

• American system (VCP) • British system (Glare Index) • European system (Luminance Curves)

• Luminance angle limit for luminaires : 45° < γ < 85° • Glare from windows can be prevented by using :

• curtains • blinds • louvers

• Glare from windows is of two types : • veiling reflections • reflected glare

• Techniques for minimization of glare from luminaires : • not locating luminaires in forbidden zone • increase light from sideways • luminaires having large surface area

• CRF (Contrast Rendition Factor) – influence of lighting on task contrast & task visibility

Task_Visibility = Given_EmmisionSphere_Illuminance

• Sphere Illuminance – Illuminance by the source providing equal luminous intensity in all directions. Also known as ESI (Equal Spherical Illuminance)

• Three categories of lighting : • general lighting • local lighting • combination of local & general lighting

• Combination of general & local lighting are preferred to avoid glare

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Tutorial Questions

• When is glare experienced?

Glare is experienced when source of light is brighter than general brightness

• How can reflected glare be avoided?

Reflected glare can be avoided by appropriate choice of interiors i.e. wall color & finish of furniture

• How can direct glare be minimized?

Direct glare can be minimized by limiting both brightness as well as light flux, normal to the field of view. Luminaires should be mounted well above the line of vision

• What is VCP?

VCP is the Visual Comfort Percentage. It is the American standard of glare evaluation.

• What is Glare Index?

Glare Index is the British standard of glare evaluation

• What level of reflectance should be maintained for walls / ceiling & furniture?

For ceiling / walls a reflectance of 0.5 should be maintained & for furniture it should be 0.25

• Why should we have long & narrow windows?

As day progresses, illumination increases in vertical plane. Hence we have long narrow window

• How can we minimize glare from windows?

• shift the work plane from the offending windows • use lightest decorative finish on surfaces surrounding window opening

• How can we minimize reflected glare?

Reflected glare from glossy surfaces can be avoided by having semi-matt kind of finish

• What are the factors that govern good general lighting?

General lighting should be based on the required horizontal illuminance. Lamps should be arranged in a regular fashion & all over the ceiling. They should be equally spaced.

• What is localized lighting? What care should be taken for localized lighting?

Localized lighting is non-uniform lighting on horizontal plane at the place of interest. Care should be taken to avoid glare as localized lighting may produce glare

• Why is it important to have general lighting ON all the time?

Localized lighting may cause glare. Moreover we should have sudden change in brightness. So we should have high level of illuminance at place of interests (localized lighting) & at other places minimum of 50% lighting (general lighting)

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Module 3

Illumination Systems Version 2 EE IIT, Kharagpur 1

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Lesson 14

Color Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

1. What are Primary colors?

2. How is color specified?

3. What is CRI? This lesson introduces concepts of color and how it is specified. Three basic elements in color perception are source of illumination, object illuminated and detector that recognizes color by the reflected light from the object. It is well known that human eye perceives between 400 to 700 nm as visible light. Radiation of a source is characterized by the Spectral Power Distribution (SPD) which affects the color of the illuminated object by way of shift in color under different types of Lamps.

Color implies different things under different contexts. Firstly at the Source color, characteristic by which an observer distinguishes patches of light of same shape and size. It connotes the Spectral Power Distribution. Perceived color, as perceived as object color. This is a result of object characteristics, viewing direction and adaptation of the observer. Lastly Object Color: Light reflected, transmitted or absorbed by a source when exposed to radiation from a Standard Light source. Normally selective absorption of incident light results in object color. However, color appearance depends on light reflected.

An important index to asses the color appearance due to a radiation from a source is Color Rendering Index (CRI). So, what is Color rendering? It is the property of making color appearance of objects under the source in question when compared to color under reference Light Conditions. This reference condition would no doubt be the conditions under natural day light conditions. From the point of view of color appearance lamps are broadly divided into three groups according to correlated color temperature. Table I lists a classification of correlated color temperature and color appearance.

Table 1

Correlated Color Color Temperature Appearance >5300°K Cool (Bluish white) 3300 - 5300°K Intermediate (white) > 3300°K Warm (Reddish white)

A good quality Lighting calls for Good Illuminance level. As illuminance level increases color temperature also increases i.e. to say whiter should be the source. Color Specification Systems Munsell system Surface colors in day light conditions are best specified according to Munsell system. According to this system color has three dimensions i.e. hue, value and chroma. Each of these dimensions

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are given a scale of values. Scales themselves being made of collection of color chips forming books of color charts. Each chart has one of the three kept constant. Hue contains five Principal Hues namely, Red (R), Yellow (Y), Green (G), Blue (B) and Purple (P). Five intermediate Hues are also used they are, YR, GY, BG, PB and RP. Value indicates lightness or brightness of the hue on a Grey Scale from (0) corresponding to black, (10) corresponding to white. Chroma is index of saturation – given in 14 steps indicates freedom from dilution with white. In munsell system, 5y 5/6, indicates yellow with half way up the Grey scale and six steps away from neutral in chroma. Sequence in specifying is Hue, value/chroma. Fig 1 shows a typical Munsell color chart for 5y5/6.

CIE System Around 1931 – mathematically exact specification of the color based on color triangle also termed chromaticity diagram was introduced. This relies on two chromaticity coordinates x and y obtained from spectral distribution of Lamp and standard colorimetric observer to three Primary colors Red, Green and Blue. Saturated Light colors are at the edge of the triangle diluting to white towards the centre.

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L ∗a ∗ b Colors Space It is the prevalent CIE system of color specification. Both Munsell and CIE are subjective and rely on visual comparison of colors differences. Standard colors observer of CIE requires objective measurements. According to L*a*b system space is defined by two mutually perpendicular axes (a & b) in a horizontal plane and a vertical axis ‘L’. Here Positive ‘a’ indicates Red content, Negative ‘a’ indicates Green content, Positive ‘b’ indicates Yellow content, and Negative ‘b’ indicates Blue content .While values along ‘L’ (in Munsell system) the value or lightness from 0 (Black) to 100 (white), a and b effect hue and saturation respectively. Color Rendering: Index Ra Index that compares color appearance of various light sources. It is based on appearance of number of test colors under different illuminants. The average shift of chromaticity when test colors illuminated by test lamp and reference source of same color temperature give a measure of color rendering. For sources having color temperature ≤ 5000°K full radiator of nearest color temperature is taken as reference. For sources having color temperature > 5000°K – simulated daylight of appropriate color temperature is used. Earlier 8 Munsell test colors of medium saturation ware used for measurement. Now fourteen test colors are employed. In these system general color rendering index Ra can have a maximum of 100 when spectral distributions are identical for both test and reference source. Some discharge lamps have spectral energy distribution is close to that of the reference source. Thus they have high color rendering, even though efficacy may be low. This lesson covered essentials of Color. Three prevelant color specification schemes are studied. Color rendering Index for is a way to assess color rendering property of any radiation. Tutorial Questions

• What are primary Colors?

Primary Colors are Red, Green and Blue

• What are the various Color Specification schemes?

Color specification schemes in vogue are Munsell system, CIE system and L*a*b Color space.

• What are basic elements in Color Specification?

Basic elements in Color Specification are hue, value and chroma

• What is Perceived Color?

Color that is perceived as object color. This is a result of object characteristics, depending on the viewing direction and adaptation of the observer

• What is CRI?

It is the property of making color appearance of objects under the source in question, when compared to color under reference Light Conditions.

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Module 4

Lighting Application Version 2 EE IIT, Kharagpur 1

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Lesson 15

Interior Lighting Version 2 EE IIT, Kharagpur 2

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Instructional Objectives • List the factors responsible for interior lighting.

• State recommended requirements for Good Lighting

• List Factors governing light output

• State Maintenance procedures for proper interior lighting

• Enumerate recommended Illuminance levels Interior Lighting Interior Lighting is a complex problem depending on various factors such as

• Purpose intended service, • Class of Interiors. • Luminaire best suited, • Color effect and • Reflection from ceiling, walls, floors.

Good Lighting means intensity should be ample to see clearly and distinctly. The light distribution should be nearly uniform over a part of the room at least. It should be diffused that is soft and well diffused. Color depends on purpose and taste source but should approach daylight / yellow. Source location should be well above range of vision. To avoid glare intrinsic brightness is reduced by diffused glass ware and by remaining objects of secular reflection from range of vision. Shadows are a must for accentuating depth but should not too apparent abruptly or dense, they are not to be harsh and should toned down. Standard practice is to have general lighting in all areas at a level comfortable to eye. It should eliminate dark shadows and avoid sharp contrast. In order to emphasize on parts that should be shown. Light sources located such that visual importance of object is kept in mind. Lamp may be concealed or counter lighted with a very low attention value to itself. Glare minimized by diffusing.

American Institute of Architects Recommends for Good Illumination.

1. General. Lighting – effectively illuminate all objects/areas with due regard to relative importance in the interior composition. Adequate for eye comfort throughout the room elimination of dark shadows and sharp contrasts – preserve soft shadows for roundness/relief – lighting emphasis on those parts that need first attention.

2. Light sources be subordinated in visual importance to the things intended to illuminate, except rarely when itself is a dominant decorative element. Unless – concealed/counter lighted, that they are not apparent they have extremely high attention value – dominate the scheme. If visible – so disposed – to attract eye to major feature of room than themselves.

3. Glare must be eliminated. Result of intense brightness in concentrated areas within the line of vision. Produced by excess brightness of visible light.

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reflection of bright lights from – Polished – low diffused surfaces - extreme contrast of light/shade Employ – means of diffusing – at source or finish the room - with Diffusing/Absorbing materials rather than reflecting material.

4. Level of illumination to be adequate for the type of eye work. Local lighting to supplement general lighting adequate illumination – working at m/cs – desks – reading tables High level local lighting is always to be accompanied by general lighting to avoid eye strain and minimize controls. If glare is avoided there is no over illumination. Natural light limits are for outdoor 107600 lux and 1076 lux for indoor. Level should be adequate for eye task expected.

5. General lighting is to be related and controlled to suit the mood. While worship, meditation, introspection need low levels. Gaiety, mental activity, physical activity or intense activity needs high levels. Theaters, homes and restaurants may need levels varied according to mood. Shops level should be appropriate to woo customers through psychological reaction. Offices, factories and schools adequate illumination to work w/o eye strain.

6. Light source must suit interior in style, shape and finish in all architectural aspects. Trends It is always taken care to keep brightest surface not greater than 3 – 4 times brightness of task on hand whereas brightness of task not greater than 3 – 4 times darkest surface. That is to say luminance ratio from brightest to darkest is 10:3:1. Eliminating glare results in good visibility, eases viewing, and creates pleasing psychological effect. All the calls for large light sources covering entire ceiling approaching sheet of light. This ensures good uniform illumination all over the room! Commonly white ceiling with semi indirect luminaires. One may employ false ceiling (white or off white) with translucent diffusing material on top of which an array of lamps are located. Major defects in lighting design are too bright luminaires, too dark floors and furniture. Preferred scheme is to have light color interiors with large sources of low brightness. Day light illumination or natural illumination, constantly changes, varies with weather, time of the day or season. Typically lower daylight levels on upper levels. This required looking into openings or windows. It is observed that at 20 – 25' from window, daylight falls below 10lx under these conditions artificial general lighting needs to be turned on. Common technique is to partially screen them, thus makes uniform general lighting. Top section of window should be as close to ceiling as possible. It controls the light to the deepest end of the room. Normally height to top window not less than ½ the depth of the room. Window area is responsible for glare. Hence termed glare are. Glare area = 1/5th the floor space. Shades, baffles, louver, diffusers are employed to control glare If ‘X’ be the artificial illuminance that is sufficient for the task on hand: natural daylight illuminance (minimum) = 2X. Say windows are located only on one wall. Width of the room less than 2 times height to top of the window is preferred. Say windows are located on the opposite walls, width between the walls not greater than 6 times height to top of the window. Location of lamps based on candle power, maximum allowable spacing, height at which located. Too great a spacing introduces dark shadows and dark spaces. Preferably lamps closer to ceiling, clear of obstructions are useful. They may be mounted on surface, suspended or recessed in the

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ceiling. Typically tasks of great visual acuity are at a plane 1.2m above floor low hanging light units are used for local lighting. In using a matrix of lamps spacing not greater than mounting height. Remembering that a plane source of light gives out light flux which produces illuminance independent of distance, mounting height is redundant when approaching a sheet of light. Interior Finish It is an important issue in interior lighting. Color reflectance – affects utilization white or off white or yellow are preferred. Typical reflectance for Ceiling is 70 – 85%, for Walls is 45 – 60%, for Floor is 10 – 20%. In addition systems need to be maintained regular by Periodic check preferably when lux levels fall by 20 – 25%, time to replace lamps. Usually luminaires are likely to collect direct light. 1½ times of minimum requirement is taken to take care of this. If voltage is maintained properly energy costs will be optimum. If voltage greater than labeled voltage, life is shortened. If voltage is less than labeled voltage, less light output results. Lamps and Luminaires are washed, cleaned. Direct lamps have less dirt, indirect lamps have more dirt. Luminaries are wiped with brush/dry cloth if necessary with a damp cloth. Grease removed by washing. Painting walls/ceiling – every 1½ - 2 years ensures good lighting levels. Clean offices may be lit using direct/indirect fluorescent lamps. Dusty smoky factory lit by mercury vapor direct or sodium vapor lamps. Replacement strategy should be related to large no. of lamps reach 70% of life preferably in a group. This lesson covered issues pertaining to interior lighting. Best thing is to approach near plane source of light. Reflectance’s of Walls, Ceiling and Floor also matter. Last but not least a good maintenance strategy is required. Lecture Summary

• Good interior lighting is governed by : • intensity (ample to see clearly & distinctly) • distribution (nearly uniform) • soft & well diffused light • color (depending on taste / purpose) • source location should be above plane of vision (to avoid glare)

• Shadows are required for actuating depth of object. It shouldn’t be too apparent abruptly or dense. Also it shouldn’t be harsh & needs to be toned down

• General lighting controlled to suit psychological moods • Natural / daylight illumination constantly varies with weather, time of day & season • We design the window opening such that the minimum daylight illuminance is twice the

artificial illuminance that is sufficient for the required task • Location of lamps depends on :

• candle power • maximum allowable spacing • height at which located • should be clear of obstruction • distribution of light required

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• Color reflectance from the interior finishing affects utilization • Interior lighting needs to be periodically checked & maintained • Lamps should be replaced when they reach 70% of its life or illumination level falls

below standard. Moreover it is preferred to change lamps in groups rather than individually.

Tutorial Questions

• What are the factors which need to be considered while designing interior lighting? • purpose of lighting or intended service • class of interiors • luminaires best suited • color effect • reflection from ceiling, walls & floor

• Why are shadows important while designing interior lighting?

Shadows are important for actuating the depth of object to be perceived

• What are the defects in interior lighting considering from brightness point of view?

Major defects from lighting systems arise due to too bright luminaires & too dark floor & interiors. So we should have light color interiors with large sources of low brightness

• What is the criteria for deciding the height of window?

If windows are located on only one wall then the height to the top of window should be greater than half of the width of room. If windows are located on the opposite walls then the height to the top of window shouldn’t be less than one-sixth of the distance between the walls.

• Why is periodic check of the interior lamps required?

Periodic check is required because the lamps need to be replaced when they reach 70% of its life or illumination level falls below standard. Moreover regular maintenance is required to clean any accumulated dust / grease / moisture.

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Module 4

Lighting Application Version 2 EE IIT, Kharagpur 1

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Lesson 16

Sports Lighting Version 2 EE IIT, Kharagpur 2

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Instructional objectives

1. List the factors responsible for sport lighting?

2. List the categories of users concerned with sport lighting.

3. State the grouping of games according to CIE. Sports Lighting This lesson addresses sports lighting application. Lighting for sports facility looks for comfort of four user groups namely Players, Officials, Spectators and Media. Players and officials should see clearly in the play area to produce best possible results the object used in the game. Spectators should follow the performance of the players. In addition to play area surroundings also need to be illuminated. Lighting should be such that it enables safe entry and exit. With increasing crowd level safety becomes more and more important. Media include TV and film, for whom lighting should provide lighting such that conditions are suitable for color picture quality as per CIE 83. This should be suitable for both general pictures as well as close up of players and spectators. Additionally, it should have provisions for emergency power supply to provide continuous transmission. Criteria relevant for sports lighting are Horizontal Illuminance, Vertical Illuminance, Illuminance Uniformity, Glare restrictions, Modeling & shadows and Color appearance & rendering Horizontal Illuminance This becomes important as major part of view is illuminated playing area. Illuminance on the horizontal plane serves adaptation of the eye. It acts as a background, so adequate illuminance is important. For safe entry and exit adequate illumination is required in the circulation area also. Vertical Illuminance Sufficient contrast across players’ body is essential for the identification of the player. This is possible only if sufficient vertical illumination is there. This is characterized by both magnitude and direction. Players need adequate vertical illumination, from all directions. Spectators and Media need illumination only in defined directions. Generally, if horizontal illuminance is taken care, vertical illuminance levels become adequate. Usually vertical illuminance is specified or measured at a vertical height 1.5 m above the play area. Apart from player recognition and picture quality vertical illuminance should enable observation of movement of ball (or object moving in the sport concerned) above the playing field by both players and spectators. Spectator’s stands are also part of the environment and must also have adequate vertical illuminance, more from the safety point of view. Illuminance Uniformity Good illuminance is important in both the horizontal and vertical planes. If it be good it does away need for continuous adjustment of cameras. This is achieved by having Illuminance Uniformity. Uniformity of illumination is expressed by two indices:

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(1). 1

Lowest IlluminanceU =Highest Illuminance

(2). 2

Lowest IlluminanceU =Average Illuminance

For best conditions of Illumination ratio of average illuminance in the horizontal plane to vertical plane should be between 0.5 and 2.0. Glare When disturbing brightness nears or enters field of view, glare is said to be there. As already caused at low levels it could cause discomfort or annoyance but can be disabling at higher levels. It is minimized by a proper choice of flood lights or luminaries, located suitably and aimed in appropriate direction. Modeling and Shadows Ability of lighting to reveal form and texture provides overall pleasant impression of players, ball and spectators. It depends on direction of the light, no. and type of light sources. Shadows from narrow beams are termed “hard” are deep. The while light from luminous side lighting termed “Flat” produce no shadows. These are two extremes and are not desirable. Later improved by few spotlights. Good quality pictures on TV require good modeling. Hence, for media to limit shadows about 60 % light must come from main camera side and 40 % from opposite side. Color Appearance and Color Rendering Good color perception is very important for complete recognition. Some color distortion is acceptable in the field but becomes important for media transmission. Color has two distinct aspects:

i. Color appearance of the light that takes care of color impression of the total environment, essentially due to the lamp.

ii. Color rendering of the light, the ability to reproduce color of an object faithfully.

Depends on spectral energy distribution of light emitted. Color appearance obtained from color temperature varying between 2000 (warmer) to 6000 (cooler) K. Color rendering is specified by CRI or Ra. Maximum possible CRI being 100, which is comparable to day light situation. Higher the Ra more agreeable is the environment. Table I lists the recommendations for various types of sports in terms of E’ Average Minimum Horizontal Illuminance and Illuminance Uniformity indices.

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Table I

Sport Level of activity

E (lux) U1 U2 Ra Tk Group

Athletics Indoor Outdoor

t/r Ca Cp t/r Ca Cp

200 300 500 100 200 400

0.3 0.4 0.5 0.2 0.2 0.3

0.5 0.5 0.7 0.3 0.3 0.5

65 65 65 20 20 65

2000 4000 4000 2000 2000 4000

A

Badminton t/r Ca Cp

300 600 800

0.4 0.5 0.5

0.6 0.7 0.7

65 65 65

4000 4000 4000

B

Basketball Indoor Outdoor

t/r Ca Cp t/r Ca

300 400 600 100 200

0.4 0.5 0.5 0.2 0.3

0.6 0.7 0.7 0.3 0.4

65 65 65 60 60

4000 4000 4000 2000 2000

B

Cricket Indoor Outdoor

t/r/Ca Cp t/r/Ca Cp

750 1500 100 200

0.5 0.7 0.4 0.5

0.7 0.8 0.5 0.6

65 65 65 65

4000 4000 4000 4000

C

Football Indoor Outdoor

t/r Ca Cp t/r Ca Cp

300 600 800 100 200 500

0.4 0.5 0.5 0.4 0.5 0.5

0.6 0.7 0.7 0.6 0.7 0.7

65 65 65 65 65 65

4000 4000 4000 4000 4000 4000

B

Table Tennis

t/r Ca Cp

300 400 600

0.4 0.5 0.5

0.6 0.7 0.7

60 60 60

4000 4000 4000

C

Tennis Indoor Outdoor

t/r Ca Cp t/r Ca Cp

500 750 1000 250 500 750

0.4 0.4 0.4 0.4 0.4 0.4

0.6 0.6 0.7 0.6 0.6 0.6

65 65 65 60 65 65

4000 4000 4000 2000 4000 4000

B

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Here t – training amateur and professional r – General recreation Ca – National competition amateur Cp – National and International competition, without media requirements E – Average minimum horizontal illuminance U1 – Illuminance uniformity Emin/Emax U2 – Illuminance uniformity Emin/Eav Ra – color rendering index Tk – correlated color temperature Group – according to CIE 83. Initial values are taken to be 1.5 times indicated minimum levels. CIE grouping into A, B, C denotes speed of action in descending order. One may observe small ball size and high speed of movement are grouped under C. These recommendations change as shown in Table II for media coverage for National TV, while that for International coverage are as shown in Table III and for HDTV as shown in Table IV Recommendations for TV (National)

Table II

Illuminance level

Illuminance vertical

Uniformity Horizontal

Color Rendering

Color Temperature

Group

Maximum Shooting distance

Main camera (lux)

Secondary camera (lux)

U1 U2 U1 U2

A ≤ 25m ≤ 75m ≤ 150m

500 700 1000

500 500 700

0.4 0.4 0.5

0.5 0.5 0.6

0.3 0.3 0.4

0.5 0.5 0.6

65 65 65

4000 4000 4000

B ≤ 25m ≤ 75m ≤ 150m

500 1000 1400

500 700 1000

0.5 0.5 0.6

0.6 0.6 0.7

0.3 0.3 0.4

0.5 0.5 0.6

65 65 65

4000 4000 4000

C ≤ 25m ≤ 75m

1000 1400

700 1000

0.5 0.6

0.6 0.7

0.4 0.4

0.6 0.6

65 65

4000 4000

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Recommendations for TV (International)

Table III

Illuminance level

Illuminance vertical

Uniformity Horizontal

Color Rendering

Color Temperature

Group

Maximum Shooting distance

Main camera (lux)

Secondary camera (lux)

U1 U2 U1 U2

A ≤ 25m ≤ 75m ≤ 150m

700 1000 1400

500 700 1000

0.4 0.5 0.5

0.5 0.6 0.6

0.3 0.3 0.4

0.5 0.5 0.6

65 65 65

4000 4000 4000

B ≤ 25m ≤ 75m ≤ 150m

1000 1400 1750

700 1000 1250

0.5 0.6 0.6

0.6 0.7 0.7

0.3 0.4 0.4

0.5 0.6 0.6

65 65 65

4000 4000 4000

C ≤ 25m ≤ 75m

1400 1750

1000 1250

0.6 0.7

0.7 0.8

0.4 0.5

0.6 0.7

65 65

4000 4000

Recommendations for HDTV

Table IV

Illuminance level

Illuminance vertical

Uniformity Horizontal

Color Rendering

Color Temperature

Group

Maximum Shooting distance

Main camera (lux)

Secondary camera (lux)

U1 U2 U1 U2

A ≤ 25m ≤ 75m ≤ 150m

1000 1500 2000

700 1000 1500

0.5 0.6 0.6

0.6 0.7 0.7

0.5 0.6 0.6

0.6 0.7 0.7

90 90 90

5500 5500 5500

B ≤ 25m ≤ 75m ≤ 150m

1500 2000 2500

1000 1500 1750

0.6 0.6 0.7

0.7 0.7 0.8

0.6 0.7 0.7

0.7 0.8 0.8

90 90 90

5500 5500 5500

C ≤ 25m ≤ 75m

2000 2500

1500 1750

0.7 0.7

0.8 0.8

0.7 0.7

0.8 0.8

90 90

5500 5500

The recommended values are average Horizontal Illuminance values to be maintained throughout operation and installation. Therefore, initial values are taken 1.25 times these suggested values. Vertical Illuminance is provided such that camera operators have free choice of camera angle. These levels are specified at a height of 1.5m above the playing area. As seen from the recommendations, Illuminance uniformity is very stringent for TV or media although human eye is less sensitive and has ability to adjust, levels of uniformity required higher for TV coverage.

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Metal Halide Lamps Most sports installations employ metal halide lamps. They are similar to high pressure mercury lamps. It contains number of metal halides in addition to mercury. Halides are partly vaporized when normal operating temperature is reached. Hence dissociates into halogen and metal in the hot central region. Radiation attains the color of the metal employed. Groups of halides include:

1) three band color radiators 2) multiline radiators 3) molecular radiators

Three band radiator are Indium (In), Titanium (Ti), Sodium (Na). Multi Line radiator are Dyspersium (Dy), Hofnium(Ho), Thalum(Tm); Titanum (Ti), Sodium (Na) and Dyspersium (Dy), Titanium (Ti), Sodium (Na). Molecular radiators are Stannic Chloride (SnCl2) and Stannic Iodide ( SnI2) Essentially improve color rendering ability of a mercury vapor radiation. Lecture Summary

1. Sports Lighting has four user groups in mind

a. Players b. Officials c. Spectators and d. Media.

2. Category of sport is made as A, B or C depending on the size of the ball/object and place of the game. “C” denotes fast paced game with small sized object.

3. Horizontal Illuminance, vertical illuminance and illuminance uniformity are crucial for this category of lighting.

4. Color appearance is very important for media coverage.

5. Considering all user groups CRI of 65 and color temperature of at least 4000K is recommended.

Tutorial Questions

• Where do we use narrow beam flood lights? • Where do we use wide beam flood lights? • Why are lamps used for sports lighting operated at higher voltage than rated voltage?

Answer to Questions of previous lecture

• What are the factors which need to be considered while designing interior lighting?

• Purpose of lighting or intended service • Class of interiors • luminaires best suited • Color effect

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• Reflection from ceiling, walls & floor

• Why are shadows important while designing interior lighting?

Shadows are important for actuating the depth of object to be perceived

• What are the defects in interior lighting considering from brightness point of view?

Major defects from lighting systems arise due to too bright luminaires & too dark floor & interiors. So we should have light color interiors with large sources of low brightness

• What is the criteria for deciding the height of window?

If windows are located on only one wall then the height to the top of window should be greater than half of the width of room. If windows are located on the opposite walls then the height to the top of window shouldn’t be less than one-sixth of the distance between the walls.

• Why is periodic check of the interior lamps required?

Periodic check is required because the lamps need to be replaced when they reach 70% of its life or illumination level falls below standard. Moreover regular maintenance is required to clean any accumulated dust / grease / moisture.

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Module 4

Lighting Application Version 2 EE IIT, Kharagpur 1

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Lesson 17

Road Lighting Version 2 EE IIT, Kharagpur 2

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Instructional objectives

1. List factors affecting Road lighting scheme.

2. State the conditions provided by Road lighting.

3. List the categories of Road and recommended light levels.

4. Understand zones in a tunnel lighting.

5. What are Post Top Lanterns? Road Lighting Road lighting provides visual conditions for safe, quick and comfortable movement of Road users. The factors responsible for the lighting scheme for roads are:

i. Luminance Level. ii. Luminance Uniformity.

iii. Degree of Glare limitation. iv. Lamp Spectra and v. Effectiveness of visual guidance.

Luminance Level As the Luminance of a road influences contrast sensitivity of drivers’ eyes and contrast of obstacles, relative to back ground. Hence affects performance of Road users. Surrounding brightness affects the adaptation of human eye. Bright surroundings lower contrast sensitivity there by requiring higher luminance for the road surface. Darker surroundings make driver adapted to road (assuming road is brighter). Roads with dark surrounds are to be lit by including surroundings. Otherwise drivers cannot perceive objects in the surroundings. CIE 12 recommends that 5m away from the road on either side should be lit by illuminance level at least 50% of that on the road. Luminance Uniformity Adequate uniformity is necessary for visual performance and visual comfort of the user. From visual performance view point, uniformity ratio is defined by U0 = Lmin / Lavg .U0 should not be below 0.4. From visual comfort view point uniformity ratio is defined as U1 = Lmin / Lmax measured along the line passing through the observer positioned in the middle of the traffic facing the traffic flow. Termed longitudinal uniformity ratio. Glare Limitation Physiological or disability glare affect visual performance. Psychological or discomfort glare affect visual comfort. Glare is to be avoided at all costs.

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Lamp Spectra Spectral composition determines color appearance of the lamp. The way lamp is going to render color to objects Low pressure sodium vapour lamps give greater visual acuity. Spectrum should be such; there is Great speed of perception, less discomfort glare and shorter recovery time after glare. Visual Guidance Visual guidance guides the road user and hence must for user to get a recognizable picture of the course immediately. This is improved by lamp arrangement that follows the run of the road. More so if turns and intersections are there. Lighting scheme must provide visual guidance. On roads having separate lanes with a separator the lighting columns are located on the separator. As is the custom in large avenues in Metros. On a curve the lighting column is located along the outer column. This gives a clear indication of the run of the road on the curvature. Visual guidance pilots traffic through lights of different colors on different routes. Exits on main roads are lit differently. Sodium vapour lamps for the main road and mercury lights for exits are employed.

Official Recommendations National standards are taken from CIE 12. Visual conditions for smooth movement and safe traffic pattern. They depend on speed, intensity, composition of traffic and complexity of the road.

Table I lists the categories of the road as A to E based on the locality and traffic density. Table II lists the appropriate recommendations for lighting.

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Road categories

Table I

Category Type and density of traffic

Type of Road Examples

A Heavy and high speed motorized traffic.

Road with separators. No crossings. Complete access control

Motorway Expressway

B Important traffic road for motorized traffic only. Separate road for slow traffic/pedestrian.

Trunk road Major road

C Heavy and moderate speed motorized traffic or heavy mixed traffic of moderate speed.

Important all purpose rural or urban road

Ring road Radial road

D Fairly heavy mixed traffic of which a major part may be slow traffic or pedestrians.

Roads in City or shopping centers, approach roads motorized traffic meets heavy slow or pedestrians.

Trunk road Commercial road Shopping streets etc.

E Mixed traffic of limited speed and moderate

Collector road between residential areas

Collector road Local streets.

Recommendations for lighting

Table II

Uniformity road Category Surrounds Luminance level. Average road

surface luminance Lav(Cd/m2)

Overall Uniformity ratio

U0 ≥

Lengthwise Uniformity ratio

U1≥

A Any 2 0.4 B1 2

Bright Dark

2 1

0.4

0.7

C1 2

Bright Dark

2 1

0.4 0.4

0.5

D Bright 2 0.4 0.5 E1 2

Bright Dark

1 0.5

0.4 0.4

0.5 0.5

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Lighting Arrangements Depending on the road category there are various arrangements for two way traffic roads. They are four types as shown in Fig. 1. They are:

a) Single sided – located on one side, if width of the road ≤ mounting height. Luminance at the opposite remote end lower than under the lamp.

b) Staggered – located on either side of the road in a staggered or zigzag fashion when width is 1 – 1.5 times the mounting height. Here care is to be taken to avoid dark patches.

c) Opposite – located opposite one another. When width is greater than 1.5 times the mounting height.

d) Span wire – luminnaires suspended along the axis of the road only normally for narrow roads. Suspended from cables strung between buildings.

a Single sided

bStaggered

cOpposite

dSpan wire

Fig. 1 Lighting arrangement for 2 way street High speed ways and dual lanes lamps may be located on the separator and are termed central twin bracket arrangement. As shown in Fig 2.

Central Twin Bracket

Central Twin Bracket and opposite

(a) (b)

Fig. 2 Lighting arrangement on the 2 Lane Roads.

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Road Junctions Special care is taken at road junctions as shown in Figs. 3 and 4. Care is taken such that junction is clearly visible from a distance. Should prevent traffic congestion. Higher luminance at junction. Using different colors at the junction. Different arrangements be for main roads and secondary roads. High mast lighting preferred at junctions.

Fig. 3 Crossing of major and minor roads roads.

Fig. 4 Crossing on a two lane highway.

Curves Special care is taken on curves. On radius larger than 300m, the curve can be treated as straight roads. Smaller radius curves, lamps are located outside of the curve. Smaller the radius, closer is the spacing. Usually 0.5 – 0.25 times that for a straight road.

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Tunnel lighting Tunnels needs to be lit both during day and night. Sense of safety same as on open road. Tunnel for this purpose is divided into five zones Access zone, Threshold zone, Transition zone, Interior zone and Exit zone. Access zone is immediately outside the tunnel, where driver must be able to detect obstacles in the tunnel. Threshold zone is first of the four zones driver in the access zone must detect, obstacles in this zone before entering the tunnel. Length depends on the maximum speed and corresponding stopping distance. Transition zone is where levels can be gradually reduced. This is where reduction takes place. Interior zone is the Tunnel stretch farthest from influence of day light. Only artificial light enables drivers’ vision in this zone. Level is constant throughout depending on the speed, here highest level is chosen. Exit zone where vision is influenced by the brightness outside. Tunnels need extra day time lighting when tunnels are very long. CIE recommendation, including various aspects, needs at least for tunnel lengths.

Tunnel lengths < 25m – no day time lighting, 25 – 125m – 50% normal threshold zone lighting and >125m – normal threshold zone lighting . Fig. 5 shows Tunnel lighting levels as a function of tunnel length.

Access Zone

Threshold Zone

Transition Interior

Exit Zone

Exit

Lexit

Lth

Entrance L20

Fig. 5 Tunnel lighting levels

Tunnel lighting employs transverse and longitudinal light distributions which are symmetrical and counter beam system, which is asymmetrical. Transverse light radiated at 90º to the axis of the tunnel may be continuous line of tubular fluorescent lamps that give good visual guidance, minimal glare and require simple switching. Only disadvantage is close spacing. Longitudinal – light radiated parallel to the tunnel axis. It leads to high efficacy and large luminaire spacing. Counter beam is light radiated parallel to the tunnel axis against the direction of traffic flow. In Residential area, road safety, security and amenity are kept in mind. Where only pedestrians are there, security and amenity are major criteria. In such areas high pressure mercury vapour lamps or blended lamps are preferred. Sodium vapor lamps of 50 / 70W have been successfully used. Wherever light needs to serve pedestrians post top lanterns are preferred.

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Transverse

Longitudinal

Counter beam

Fig. 6 Scheme for Tunnel lighting.

Summary

• Road lighting aims safe, quick and comfortable movement of traffic. • There are five categories of Roads, A, B, C, D and E depending on the type and density

of traffic. • Mostly sodium vapor lamps are preferred on the roads. • At junctions mercury vapor lamps may be provided. • Tunnel lighting needs to be carried out in such a way as to gradually change the light

level. Tunnels lit during the day as well as night. • Residential areas have post top lanterns.

Tutorial Questions

• What are the factors responsible for road lighting? • What are the various arrangements of locating lamps on roads? • What are the various categories of the roads? • List the various zones in a Tunnel from lighting view point • What are the various schemes employed for tunnel lighting?

Answer to Questions of previous lecture

• Where do we use narrow beam flood lights?

Narrow beam flood lights have higher light flow. So they are used where greater distances are involved.

• Where do we use wide beam flood lights?

Wide beam flood lights have lower intensity. So they are used where large areas are involved.

• Why are lamps used for sports lighting operated at higher voltage than rated voltage?

A small increase in voltage produces higher light output & comparatively less increase in power consumption. Hence they are operated with voltage greater than rated voltage

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Module 4

Lighting Application Version 2 EE IIT, Kharagpur 1

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Lesson 18

Lighting Calculations Version 2 EE IIT, Kharagpur 2

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Instructional Objectives • List the issues for Lighting Calculations

• Learn the quick way of estimating recommended levels

• Understand the use of Iso-lux diagrams

• List the factors to be accounted for calculation

• What is room index Lighting Calculations In order to do calculate, manufactures manuals data sheets are the first source. For the Engineer/Architect several softwares, fast, accurate and convenient are available which rapidly assess requirements on field. One should be able to check if software is giving right solution! This needs understanding of long hand calculations discussed in this lesson. Various issues involved are Illuminance – horizontal and vertical may be got from Tables. Also given in the form of graphs, called Isolux diagrams. The other issue is the Luminance of the source in question. Horizontal Illuminance Specified as Average illuminance on the work plane while Sitting 0.75 – 0.9m above floor and while Standing 0.85 – 1.2m above floor.

Thus , where totarE = U.F. × M

E = Average horizontal illuminance in lux. φ = Total light output in Lumens. A = Area in m2 U.F = Utilization factor M = Maintenance factor

Ceiling

4

1

3322

3 3Lam

walls walls

Work plane

Frieze (wall area above luminaire plane)

Floor 1 – work plane, 2 – wall area below the luminaire, 3 – on the frieze, 4 – ceiling

Fig. 1 Schematic showing various zones in an interior of a room.

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Utilization Factor UF depends on Light distribution of luminaire, Reflectance of ceiling, walls and Room Index K. Room surface reflectance which depends on the dimensions shown in Fig. 1 is specified in the form of reflectance code as given in the next section Reflectance code Code 7751 connotes a reflectance from Ceiling of 0.7, Frieze of 0.7, Walls of 0.5 and work plane of 0.1. Similarly 751 denote reflectance from Ceiling of 0.7, Walls of 0.5 and Work plane of 0.1. That is to say there is no frieze at all. If not known or available average value of 753 is taken for a room with light colors.

If l = length, b = breadth then the hm = Mounting height of luminaires.

m

lbk =h (l + b)Room Index

Table I lists the minimum number of luminaries required for different room indices, if there be M luminaries length wise and N luminaries width wise.

Table I

K 0.6 0.8 1.0 1.25 1.5 2.0 2.5 3.0 4.0 5.0 M 2 2 3 3 4 4 5 6 8 10 N 1 2 2 3 3 4 4 4 5 6

Direct component at a point p due to a point source is as already discussed is shown in Fig. 2 and that due to a line source is shown in Fig. 3.

hm

pa

d

α Iα 3αp 2

m

IE = cos αh

Fig. 2 Illuminance due to a point source Linear source of infinite length

α hm

hm

αp

π I C o sαE =2 d

α

m

π I = C o sα2 h

Fluorescent lampFig. 3 Illuminance due to line source.

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Calculating from Isolux diagram involves no of steps. Let us consider source placed at P be a point source. Then place the Isolux diagram on that plane.

Step1. From the luminous intensity table for the luminaire calculate illuminance on the working plane and distances to each point. Step2. Plot E and a using this 2 illuminance distribution curves draw isolux curves as shown.

Step3. Extend to four quadrants using tracing or transparent paper. Then Step4. Place isolux diagram on the plan of the luminaire layout. Positioning: centre over the point of interest. Sum the illuminance. Step5. If 1000 lumens per luminaire is assumed, n

pEE =

N = no. of lamps per luminaire

1000φ

E = value from step 4.

1

7

32

4

8 9

6

60402010 5 lx

5P 40

10 5

5

5 – 40 4 – 5 8 – 10 9 – 5

Epe 594 n = 3 3300 = φ

Fig. 4 Typical Isolux diagram

Indirect component at ‘p’ av

indn avF 1- e

φ

∑eE =

φ = light flux leaving in lumens.

∑Fn = total area of the room surfaces

eav = average reflectance of the surface. n n

av

e F

nF∑e = ∑

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Where en = reflectance of the nth surface Vertical Illuminance It becomes important in case of an Average wall, wall mounted object, black board – chalk board and wall display in a shop.

Illuminance is given by

tot

av wE = (R)n MAφ

Where φ = Luminous Flux – Lumens, A = Area of the work plane,

(R)Nw = U.F, M = maintenance Factor.

Figure 5. shows the vertical illuminance at a point ‘P’ Direct component at a point P

h

pa

d

α Iα 2αp 2

IE = Cos α Sinαh

Fig. 5 Vertical Illuminance due to a point source At any point total Illuminance due to all luminaries is given by EP (total) = E1 + E2 + …+ En

Linear sources Permanent length

pπIαE = Sinα Cosα Infinite Length2h

2πIα= Sin α

2a αI =

9.25Finite Lengthφ

Luminaire Luminance

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A ν

Ah

Fig. 6 Luminaire Luminance Calculation ν

νν

IL = A→

pparant areaAA Cosν + A inνν h νA = S

1000 Lumen – 0 < ν < 85º

Lecture Summary

• Illuminance level depends on the nature of working environment & is specified in terms of horizontal, vertical & inclined illuminance. These are obtained graphically from numerical tables.

• Isolux diagrams are used for calculation of illumnance & luminance levels • A room can be divided into four zones for calculation of illumination level :

• work plane • wall area below luminaire • on the fieze (wall area above luminaire) • ceiling

• Horizontal illuminance is given by:

totavgE = × UF× M

• Utilization Factor (UF) depends on: • light distribution of luminaire • reflectance of ceiling / walls

• Room index (k) is given by :

m

l×bk =h ×(l + b)

• Vertical Illumination is given by:

• Luminaire Luminance is given by: Where Aγ is the apparent area in the specified direction & is given by

totavgE = ×

Aφ UF× M

γγ

γ

IL =

A

γ h vA = A ×cosγ + A ×sinγ

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Tutorial Questions

• What do you mean by surface reflectance of 7751 & 751? • What are isolux diagrams? • What do you mean by fieze?

Answer to Questions of previous Lecture

• What is silhouette?

It is brightness towards the observer rather than illuminance on the road surface.

• Why do lamps have asymmetrical light distribution on roadways? How is it achieved?

We have light directed towards the street only with ample light on the pavement to enhance the aesthetics of the buildings & lower level of lighting on the street. Asymmetrical distribution is achieved by use of reflectors, refractors & prisms.

• On what factor does the arrangement of luminaires depend?

It depends on the electrical aspect. We may have one side or opposite or staggered lighting depending on the number of circuits available. Optimization is achieved by using double lamps at middle of road.

• What is the importance of supplementary lighting in tunnels?

While entering or coming out of the tunnel drivers may face problem due to abrupt change in brightness. So supplementary lighting are used to avoid abrupt changes.

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Module 4

Lighting Application Version 2 EE IIT, Kharagpur 1

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Lesson 19

Lighting Applications Version 2 EE IIT, Kharagpur 2

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Instructional Objectives

• List various lighting applications

• Understand the need to integrate lighting with other applications

• Classify Industrial Lighting

• Classify Office Lighting

• List requirements of lighting for Educational Institutions, Auditoria, Hospitals, Hotels and restaurants

Lightning Applications This lesson presents various issues pertaining to lighting applications. First area of application is Industrial. Here Wide range of visual tasks are involved compared to schools or offices. Involves Extremely small to very large objects. The objects or areas could be Dark or light with Flat or contoured surfaces. In industrial environs the tasks are graded according to degree of fineness. Less critical tasks require low level/quality of light Finer work requires high level with minimum glare. General lighting is usually supplemented by specific lighting. Lighting is dictated by Nature of work, Shape of the space and ceiling structure

Thus lighting in Industry is Classified as:

• single storey without skylight • multi storey • single storey with sky light • high bay

Single storey without sky light, specially in Work shops or factories floor to ceiling height is kept around 3m or 5 m or 7 m. Fluorescent lamps are used up to a mounting height of 5m arranged in Continuous or broken rows. They may be mounted directly on ceiling or suspended. When Mounting height hm > 5m, usually discharge lamps with reflector luminaries are employed separation distance S < 1.5hm. Usually line of luminaires is mounted perpendicular to work benches. Normally trunking systems containing wires enables efficacy of illumination. Multistorey Ussually Smooth white ceilings with height in the range 2.8m < h < 3.5m. Here Roof acts as extended reflector. They use Tubular fluorescent lamps in continuous or broken rows. The lighting is Integrated with a/c system.

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Single storey with skylight

Fig. 1 Typical Single storey with Sky light When using Lantern roof uses saw toothed roof, to allow more of day light Employs Reflector type luminaires in a row perpendicular to work bench. In High bays, where ceiling height h > 7m, light sources need to be mounted higher. This facilitates avoiding obstruction to guide rails of cranes and tall machinery. Here, Dispersive narrow beam reflector luminaries fitted with metal halide or high pressure sodium vapour lamps that are color corrected are used. Special Tasks in Industrial Environment Best way of assessing Visual requirement is known by doing it one self. Lighting design should Create necessary contrast between the details to be distinguished against the background. If general lighting does not meet these requirements then additional aids such as Illuminated magnifying glass, Stroboscopic lighting for viewing objects in motion or Monochromatic light in glass and ceramic manufacture. Office lighting As regards office lighting they can be categorized as General offices, Private offices, Conference rooms. Here usually Limited well defined visual task are involved. Typically there are Horizontal work planes at 0.75 – 0.85m from the floor. Typical Ceiling heights are 2.8 – 3m. Illuminance Recommended Illuminance levels in Small offices are 500 – 750 lx on the task and in Large office 750 – 1000 lx on the task. General lighting at least equal to 50% of task illuminance with a minimum of 400 lx is recommended. Luminances Recommended luminance values for Walls is 50 – 150 Cd/m2, for Ceiling 100 – 200 Cd/m2 and for Tasks / Task area 100 – 300 Cd/m2. Color appearance should be agreeable. All this easily obtained using Day light fluorescent lamps with louvers and diffusers.

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General offices They usually have Moderate to large area where work planes are not fixed. Such areas Ceiling mounted / recessed luminaries are arranged in a regular pattern. Lighting is suitably combined with air handling systems. This may be using false ceiling or suspended ceiling, hence luminaries should be well ventilated. Since large areas are involved energy saving by localized lighting by having appropriate controls for switching keeping lighting recommendations in mind.

It must be mentioned that Visual display units need special care such that Windows / sources do not reflect on the screen. Typically recommended levels are 400 lx for light screen and 700 lx for dark screen. Similarly for private office and conference rooms. As Drawing offices involve precision work a min. of 1000 lx is recommended In Educational Institutions where Writing, reading & reading black board are main tasks, Levels for Office lighting with additional lighting for blackboards are sufficient. Recommended levels for Class room are 300 – 500 lx, for Handcrafts room – 500 – 1000 lx, for Laboratories – 500 – 1000 lx. Optics laboratories need special lighting as dictated for the experiments in optics. On chalk boards or Blackboard, level should be 300 – 500 lx (vertical). In Auditoria (during projection) 50–150 lx otherwise 300–500 lx. Needless to mention that in auditoria Reading writing require 500 lx. Care is to be taken to prevent glare. There is a need to provide Dimmers to vary the lighting level. There should be additional Local lighting on the blackboard. For proper functioning Centralized controls are required. The Control panel should be easily accessible to Lecturer at the rostrum. Table I lists the recommended levels for shops and stores. Shops and Stores

Table I

Interiors large shopping centers lx Other areas lx General lighting 500 – 750 300 – 500 Local lighting 1500 – 3000 750 – 1500 Show case/windows General lighting 1000 – 2000 500 – 1000 Local lighting 5000 – 10000 3000 – 5000

Show case in a store must be lit such that it brings out special features of the product. Hardware can use diffused fluorescent lamps. Jewellery best lit by incandescent lamps.

Hotels / Restaurants In hotels and restaurants lighting must take care of Approach roads / car parks / main entrance. They are lit by Columns – 30cm to 12m high. They are termed post top Lanterns. EH = 10 lx. canopy EH = 100 lx. Entrance halls, foyers attention is to be drawn to reception. Desk Hence increase illuminance around reception. Lighting system should be Flexible. In restaurants Fluorescent lamps around the perimeter of dining area with local lighting at tables (lowered at night times). This needs Dimming and partial switching. Eav = 100 lx is recommended. No doubt at Cash desk, higher level of 300 lx is preferred.

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In Corridors and stairs, when having Long corridors without any daylight Fluorescent lamps are preferred with Day time Illuminance of 150 lx and Night time Illuminance of 75 lx. In addition hotels must have all night pilot lighting and provisions for Emergency lighting In Bed Rooms or Guest rooms provisions must be there for General lighting, Reading lamp at the table Bed head reading lamp in wall brackets mounted high. Mirrors should be lit by Fluorescent lamps right above or on either side.

Table lamp.

Standard Light.

Bed head lamp.

Mirror lamp.

Fig. 2 Arrangement in a typical Guest Room in a Hotel Hospitals Lighting in hospitals is from the view of Patients, Technicians and Doctors. In this application Color rendering is important. Changes in color may misdiagnose a disease and effect psychology. Radiation is employed for treatment interference free. In Patients room General lighting recommended is 100–200 lx and Local lighting recommended is 100 – 300 lx. Luminance 350 cd/m2 Examination lighting level should be 1000 lx. Night light should at least be 0.5 lx. Night observation light suggested is 5 – 20 lx. Recommended levels for Corridors during day are 200 – 300 lx. and nights is 5 – 10 lx. Lights recommended for Exam rooms are 4000ºK fluorescent lamps with 500 – 1000 lx. Theaters should have shadow free lighting. ICU and X Ray rooms should have at least 10 – 30lx. Before, we close this lesson some types of luminaries employed are illustrated. Figures 1 to 4 show various types of luminaries that may be used for various types of lamps shown in Fig.5

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Fig. 1 Typical Decorative Surface mounting Consumer Luminaires

Fig. 2 Typical Consumer Luminaires for Flourescent Lamps surface mountable

Fig. 3 Typical decorative Downlighters using CFL which can be recessed in ceiling

Fig. 4 Typical Commercial Luminaires using CFLs suitable for recessed mounting

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Fig. 5 Typical Spectrum of Lamps

Lecture Summary

• Industrial lighting is dictated by: • nature of work • shape of space • ceiling structures

• Industrial lighting can be classified as: • single storey without skylight • multistorey • single storey with skylight • high bay light

• Additional lighting are used if general lighting doesn’t meet requirements viz. illuminated magnifying glass, stroboscopic lighting, monochromatic light etc.

• Fluorescent lamps with louvres & diffusers are preferred for office lighting • Vertical illumination becomes necessary for blackboards in educational institutions • In hospitals lighting is done according to convenience of patients, technicians & doctors.

Operation theatres need shadow free lighting. ICU & X-ray rooms have low luminance levels.

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• In shops, restaurants & other commercial places, local & color lighting is employed to highlight a particular place / product

Tutorial Questions

• When do you need stroboscopic lighting? • What care should be taken for auditorium lighting? • How should be the line of luminaires be mounted in industries & why?

Answer to Questions of previous lecture

• What do you mean by surface reflectance of 7751 & 751? • 7751 has surface reflectance of ceiling = 0.7, freze = 0.7, walls = 0.5 & work

plane = 0.1 • 751 has surface reflectance of ceiling = 0.7, negligible for fieze, walls = 0.5 &

work plane = 0.1 • What are isolux diagrams?

Isolux diagrams are used for calculation of illuminance & luminance levels

• What do you mean by fieze?

It is the wall area above the luminaire plane i.e. the plane at which luminaires are located

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Module 4

Lighting Application Version 2 EE IIT, Kharagpur 1

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Lesson 20

Conclusions on Illumination Engineering

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This lesson is to conclude the first part of the course on Illumination Engg. It recaps the summary of material covered under Illumination Engineering. This forms the 50 % of the course. Nineteen lessons covered need for lighting, behavior of eye, Principles of artificial Lighting, Measurements, calculations & Applications. Figure 1 shows the typical inputs necessary to a person dealing with Illlumination Engg. to make it useful to the humanity.

First lesson stressed the need for lighting .Good lighting aims so that our eyes clearly and pleasantly perceive things. Invariably artificial lighting schemes use some form of physical phenomena. All lighting sources today employ electrical energy. Electrical Energy sources may be DC or AC single phase or three phases. Usual Sources of electrical energy are Hydro & Thermal. Usually load is unbalanced for a practical 3-phase system. Radiation Second lesson deals with radiation. Light is the Radiant energy that provides visual sensation. Human eye can sense over the 380nm (violet) to 700nm (red) wavelength.. Maximal relative energy content of sunlight around 550 nm coincident with maximal luminosity of human eye. Artificial light sources employed may be broadly categorized as Incandescent Lamps and Gas Discharge Lamps. These are based on the following four Physical Processes:

• Incandescence • Luminescence • Fluorescence • Phosphorescence

However, we learn as we go along that Good efficient lighting is obtained by combining luminescence & fluorescence. Having learnt about necessity of artificial Illumination and radiation characteristics, it is time to look at how the eye responds.

Usefulness To

Humanity

Physiology Psychology

Math Chemistry

Physics

Economics

Art

IllumEngineerin

ination g

(Aesthetic)

Fig. 1 Inputs necessary for Illumination Engg

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Eyes & Vision A human eye resembles a camera in structure and function. Important parts of a human eye are Iris / pupil, Lens and Retina. The vision is either Photopic (dealing with fine image details and color discrimination, due to cone cells) or Scotopic (functions in dim light and no image details, due to rod cells). It may be mentioned that Human eye is achromatic in nature. Dispersive power of human eye is little greater than water. Eye is subject to Purkinjee Effect essentially dealing with shift of luminosity and ability of eye to adjust. Best sensitivity of cone cells is around 550nm (i.e. yellowish green hue) and that for rod cells is around 507nm (i.e.bluish green). Good lighting scheme should aim at Prevention of defective vision, Optimization of resources and improving conditions of visibility. Visibility depends on the (Observer Issues) size / details of object, level / quality of illumination, contrast / color and available time. It also depends on efficacy of individual, one’s eye defects, optical / physical fatigue and distraction. The Causes of fatigue could be rotating source, focusing on the source of glare, reading double impression. Usually after a days work pupil is dilated a nights rest offsets fatigue due to a days work.Visibility reduces due to eye defects and fatigues. Eye defects are caused due to aging, use or abuse. Hence, good illum0ination looks for producing clear and quick images. Illumination affects physiology as well as psychology, hence quality lighting is important. Factors governing illumination quality are glare, diffusion, direction / focus, composition and distribution. Minimum lighting required for good visibility is 100 ft-cd or more. For good visibility, brightness of surrounding should be greater than 0.01 ft-L & also should be less than that of the test object. Apart from illumination, visibility is talked in terms of visual acuity, visual efficacy, visual speed and visual health.

Acuity is the ability to distinguish details depending upon: brightness of the object, characteristics of light entering the eye, contrast maintained. With age there is a reduction of visual activity, decrease in size & elasticity of pupil, decrease in flexibility of optic lens there by leading to higher levels of illumination requirement. Monochromatic light has good acuity producing distinct images on retina and details are distinguished well. Combination of different colors reduces acuity which is known as Chromatic Aberration. Color sensation by eye has a lag which depends on presentation & cessation of stimulus, rate of rise / fall of sensation (different for various colors) and nature of simultaneous colors & combination of colors Laws of Illumination Next lesson deals with quantification Illumination. Unit of luminous intensity is Candela (Cd), it is the luminous intensity of a surface which is1/600,000 of a blackbody, at the solidification temperature of Platinum (1773 °C) under standard atmospheric pressure. Luminous intensity over 1 steradian solid angle by a source of 1 Cd is called as 1 lumen of light flux (lm). For a point source one talks of MSLI or average intensity x solid angle (mean spherical Luminous intensity). Hence, Luminous Flux = luminous intensity × solid angle. Illuminance is luminous flux per unit area. Frechner’s Law states that the same percentage change in stimulus calculated from the least amount perceptible gives the same change in sensation. Inverse Square Law states that the intensity of illumination produced by a point source varies inversely as square of the distance from the source.

• Lambert’s Cosine Law of Incidence –

2

I×cosαE =D

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• Lambert’s Cosine law of Emission – Im = I × cosα Photometry The next lesson deals with Measurement issues. This is necessary before using any lamp source. This involves comparing it with a primary standard (standard lamp) using a photometric bench. This comparison may be carried out by varying position of standard lamp, by varying position of test lamp or by varying position of the screen on the photometric bench. The lesson also addresses issues pertaining to direction of light. Luminnaires are used for directing the light from a source of light in the desired direction. Types of luminaires employed may be broadly categorized as directed reflectors or diffusing. Incandescent Lamps Having covered generics, we take now each type of lamp in the subsequent lessons. As the name suggests Incandescence employs radiation at high temperature. Incandescent Lamps called Type-B employ tungsten / osmium / tantalum filament, in vacuum, where as those called Type-C: tungsten filament, in inert gas (generally a mixture of Ar & N2). Tungsten being ductile in nature, having high melting point & high radiation efficiency has been widely in use as filament material. However, at higher wattages the filament tends to evaporate and darken the bulb known as lamp darkening. Use of inert gas in incandescent lamps helps in decreasing the rate of evaporation of tungsten & improves efficiency. Further it is observed that higher efficiency is obtained when incandescent lamps are operated at low voltages. Filament characteristics depend on filament length, filament diameter, coil spacing, lead wires, method of mounting, no. of supports, properties of gas employed , gas pressure, bulb size and shape of bulb. Usually Bulbs are designed for uniform radiation, accurate consumption of power, good efficiency and reasonable rating of life. The most common lamps employed fall under the category of Discharge Lamps, this is covered in the next three lessons. Discharge Lamps I This lesson introduces discharge lamps. They either use Luminescence which produces light radiation by chemical / electrical action on gas / vapor or Fluorescence where in radiation is absorbed at one wavelength & radiated at another wavelength with in visible spectrum. It is to be noted that in lighting arrangements a combination of luminescence & fluorescence increase efficiency far beyond incandescence. Efficiency is measured in terms of lumens per watt of power consumed. Thus discharge lamps consist of discharge of electricity through a tube containing a conducting medium. Conduction is by way of electrons. Types of electron emission may be Electric Field Emission, Thermionic Emission or Photoelectric Emission. So in a discharge lamp gas / vapor is made luminous by an electric discharge whose color / intensity are dependent on gas / vapor used and intensity to some extent proportional to current. Broadly discharge lamps are of two categories 1) Mercury Vapor Lamps, 2) Sodium Vapor Lamps. Mercury vapor lamps tend to give a light bluish green color (deficient in red color). They have a starting electrode provided to initiate the arc. After a run-up time of typically 2 min., mercury vapor discharge starts. Gas at high pressure improves the CRI (color rendering index) of mercury

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vapor discharge lamp. With Sodium vapor lamps a pre-heating heater is provided. The lamp glows initially with red color (Neon -vapor discharge which is used as initiating gas) & then turns to orange yellow arc (Sodium vapor discharge) Discharge Lamps II Low pressure Sodium vapor Lamp has outer envelope of inner surface is coated with Indium Oxide & that acts as an IR reflector. While high pressure mercury vapor Lamp gives rise to bluish white line spectrum, together with some phosphors improves color. If some luminescent powder is put in the tubular lamps it enhances brilliancy of light Radiation from Low Pressure Hg-vapor lamp (which is in the UV-region) is impinged on luminescent materials, they reradiate at longer wavelength of visible spectrum. This is the principle of Fluorescent Lamps. Various types of Fluorescent Lamps Day Light Lamp, Standard White Lamp and Soft White Lamp. Factors deciding the dimension of fluorescent lamps are luminous efficiency, brightness, lumen output, lumen maintenance and reliable starting. The voltage rating of the lamp is decided by arc length, bulb diameter and lamp current. Discharge Lamps III As already discussed fluorescent lamps are Low Pressure Mercury vapor lamps. For a given current & tube diameter of fluorescent lamp we have voltage directly proportional to length, inversely proportional to diameter and inversely proportional to current through discharge tube. By a T12 fluorescent tube we mean that a tube with diameter of 12 × (1/8)” i.e. 1.5”. Radiation output from a fluorescent tube is directly proportional to the current density in the tube. Fluorescent lamps emit a considerable amount of UV & IR radiation along with visible radiation. UV radiation is converted to visible light using phosphors. There are beneficial applications. UV radiation is beneficial in small quantities. Applications of UV radiation are water purification, detoxifying bacteria, curing of diseases, dye & food processing and employed in producing Vitamin-D in food sources.

Compact Fluorescent Lamps (CFL) are compact, efficient, energy saving, having higher lifetime with reasonably good CRI & near daylight illumination characteristics. Moreover they have all the accessories inbuilt. Hence they are better than traditional fluorescent lamps in terms of economy and efficiency. Illumination Systems I Now using the lamps discussed so far lighting system needs to be developed. These are termed Illumination Systems. This lesson discusses the issue. Illumination system comprises of a lamp (the artificial source of light), luminnaires & the control gear. Commercial luminnaires can be categorized into general or industrial. Luminnaires are also characterized by the way they control & direct light i.e. luminous intensity, luminous distribution and number of lamps. Although use of mirrors in luminnaires are avoided as they cause glare modern luminairres do have properly positioned mirrors to act as reflectors. Efficiency of a luminnaire is talked in terms of light output ratio (LOR). This includes both downward as well as upward light. Practically DLOR (downward LOR) is of importance. Luminnaires for hazardous areas should maintain temperature and are hence encapsulated to resist pressure. Gasketted luminnaires which are

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completely sealed takes care of handling moisture & dust. Emergency lighting should have self supporting power system to provide lighting when normal lighting fails. Illumination Systems II The II part on Illumination systems addresses control gears. Control gears are the accessories that help in controlling the requisite amount of light flux on the work plane. Gas discharge lamps are constant current devices. Constant current is achieved by use of ballasts. Requirements for good ballasts very less undue power loss, should offer high impedance to audio frequency, should suppress EMI / RFI / TVI, should provide proper starting conditions and should have as high power factor as possible. To improve power factor capacitors are used in series. Excepting high pressure mercury vapor lamps, all lamps have starting voltage more than spark over voltage, hence require starters & igniters to be used as starting devices. Igniters are small three electrode devices which are fired by controlled pulses from small electronic circuits. Apart from local & general lighting dimmers / timers are used in lighting systems to have good control and direction of light. Glare

This lesson discusses all important issue of glare, which affects the performance of lighting system. By definition Glare is the brightness within the field of vision. Effects of glare injures the eye, disturbs the nervous system, causes annoyance, discomfort & fatigue, reduces efficiency of work, interferes with clear vision and risk of accident increases. Glare could be direct bright luminaire in the field of vision or Reflected Glare due to reflection from a glossy surface. Reflected glare causes more annoyance than direct glare. Direct glare can be minimized by mounting luminaires well above the line of vision. When glare level impairs the vision, it is said to be Disability Glare. If eye is subjected to glare for a long time results in Discomfort Glare. Glare Evaluation Systems in vogue are American system (VCP), British system (Glare Index) and European system (Luminance Curves). Luminance angle limit for luminaires is between 45° < γ < 85°. Other source of glare being windows. It is of two types i.e. veiling it can be prevented by using curtains, blinds or louvers. Reflections and reflected glare. The Techniques employed for minimization of glare from luminaires are not locating luminaires in the forbidden zone, increasing light from sideways or using luminaires having large surface area. In addition CRF (Contrast Rendition Factor) – influence of lighting on task contrast & task visibility. By definition Task Visibility is the ratio of Given Emission and Sphere Illuminance. Where Sphere Illuminance is the Illuminance by the source providing equal luminous intensity in all directions. Also known as ESI (Equal Spherical Illuminance). All this means three categories of lighting are required they are general lighting local lighting and a combination of local & general lighting. Combination of general & local lighting are preferred to avoid glare Color Next lesson deals with issues pertaining to color. Three Components of Color Perception are Source of Illumination, Object Illuminated and detector. Source color tells us about spectral

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power distribution of the light source. Object Color denotes appearance of the object due to selective appearance of incident light. Perceived Color is a result of object characteristics together with viewing conditions. Color characteristics are assessed by Color Rendering Index (CRI). CRI is appearance of an object under test source in comparison to appearance under standard light conditions, like those under natural day light conditions. Color standards follow Munsell system or CIE system. Interior Lighting Next lesson discusses recommendations pertaining to interior lighting. Good interior lighting is governed by intensity (ample to see clearly & distinctly), distribution ( maintained nearly uniform), using soft & well diffused light, color (depending on taste / purpose) with source located well above plane of vision (to avoid glare). Although shadows are required for actuating depth of the object. It shouldn’t be too apparent abruptly or dense. Also it shouldn’t be harsh & needs to be toned down. General lighting controlled to suit psychological moods. Natural / daylight illumination constantly varies with weather, time of day & season. We design the window opening such that the minimum daylight illuminance is twice the artificial illuminance that is sufficient for the required task Location of lamps depends on candle power, maximum allowable spacing, height at which located, position of obstructions ( if any) and required distribution of light. Color reflectance from the interior finishing affects utilization. With all this like any other system interior lighting needs to be periodically checked & maintained. It is advisable that lamps are replaced when they reach 70% of its life or when illumination level falls below standard level. Moreover it is preferred to change lamps in groups rather than individually. Next important issue pertains external lighting. This consists of Sports lighting and Road Lighting. Sports Lighting This lesson details sport lighting recommendation. Sports Lighting has four user groups in mind Players, officials, Spectators and Media. Category of sport is made as A, B or C depending on the size of the ball/object and place of the game. “C” denotes fast paced game with small sized object. Horizontal Illuminance, vertical illuminance and illuminance uniformity are crucial for this category of lighting. Color appearance is very important for media coverage. Considering all user groups a CRI of 65 and color temperature of at least 4000 K is recommended. Road Lighting This lesson looks into Road Lighting recommendations. The aim of the Road lighting is for safe, quick and comfortable movement of traffic. From this view point, there are five categories of Roads, A, B, C, D and E depending on the type and density of traffic. Mostly sodium vapor lamps are preferred on the roads. At junctions mercury vapor lamps may be provided to highlight the junction.. Tunnel lighting also needs to be carried out in such a way as to gradually change the light level. Tunnels are lit during the day as well as night. Residential areas usually employ post top lanterns

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Lighting Calculations This lesson discusses lighting calculation methods. No doubt, today there are many software packages are available, but one needs to have a physical basis of assessing the results. Therefore, it is necessary to know how manual calculations are done. Illuminance level depends on the nature of working environment & is specified in terms of horizontal, vertical & inclined illuminance. These are obtained graphically from numerical tables. Isolux diagrams are used for calculation of illumnance & luminance levels. A room may be divided into four zones for purposes of calculation of illumination level as work plane, wall area below luminaire, on the frieze (wall area above luminaire) and ceiling Horizontal illuminance is given by:

totavgE = × UF× M

Utilization Factor (UF) depends on light distribution of luminaire and reflectance of ceiling / walls

Vertical Illumination is given by: totavgE = × UF× M

Luminaire Luminance is given by: γγ

γ

IL =

A

where Aγ is the apparent area in the specified direction & is given by γ h vA = A × cosγ + A ×sinγ Lighting Application Having had a look at all aspects of lighting this lesson looks at lighting applications. Industrial lighting is dictated by nature of work, shape of space and ceiling structures. Industrial lighting is classified as single storey without skylight, multi storey, single storey with skylight or high bay light. Additional lighting is used if general lighting doesn’t meet requirements viz. illuminated magnifying glass, stroboscopic lighting, monochromatic light etc. Fluorescent lamps with louvres & diffusers are preferred for office lighting. Vertical illumination becomes necessary for blackboards in educational institutions. In shops, restaurants & other commercial places, local & color lighting is employed to highlight a particular place / product. In hospitals lighting is done according to convenience of patients, technicians & doctors. Operation theatres need shadow free lighting. ICU & X-ray rooms have low luminance levels. Some of the Indian Standards for lighting application are also covered in this lesson. Details can be had from hand book of BIS. Mostly adopted from CIE

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