Hand Book Illumination

8/9/2019 Hand Book Illumination

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Lesson

1

IntroductionVersion 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 andlasers.

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 andsignaling neon signs, LED LCD displays beacons and lighting for surveillance.

Utility services for large building/office complex and layout of different meters andprotection 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 fromabout 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 sourceemploying 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 ofprofessionals 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 ofthese 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 inmind, 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

MathChemistryPhysics

Economics

Art(Aesthetic point)

PhysiologyPsychologyMedicine

IlluminationEngineering

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, minimizingthe 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 Teichmullers definition

for lighting. We say the lighting is good, when our eyes can clearly and pleasantly perceive thethings 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 areaware, 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 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 highvoltages.

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 asan alternative.

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

Xmission line132/220/400 kV

400

V

~

Generator11/33 kV

Fig. 2 Typical Power System

Distribution line66/33/11kV

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 isthree 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.

564V

1

tmsms

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 anyflux. 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 from horizontal resolving AL , we have , AM

Horizontal Component, AN Perpendicular Component.

oMLA = 90 - MAL = MAO =

AM = AL sin = v sin

AN = AL cos = v cosWe know E.m.f generated in A is only due to AM perpendicular to magnetic flux density

- B- If be the length of the sides A and B

e.m.f generated on one side =

Bv sin volts ..( 1 )

R

N

B

A

S

Fig. 4 Single Phase Generation



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A

o

b

L

B

0

M

L

A

N

90

Fig. 5 Single Phase Generation

Total e.m.f. generated = 2Bv sin .( 2 )if = 90. Coil is vertical. E.m.f. generated is maximum.

Em = 2Bv ..( 3 ) or in other words

e = Em sin ...( 4 )

Let b = breadth of loop

n = speed of rotation in r.p.s

then v = bn m/s

Em = 2Bbnv = 2BAn = A = Loop areaIf coil of N turns replaces the loop

Em = 2BAnN ..( 5 )e = Emsin = 2BAnNsin ... (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 havesame amplitude as in RR1 but lag by 120 and 240 respectively. Generated voltages in

three coils are



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eR= Em sin

eY = Em sin( 120) andeB = Em sin( 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 RR1Finish

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 asshown 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. 11What 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

.

ZZ

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 orunderground 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

MathChemistryPhysics

Economics

Art(Aesthetic point)

PhysiologyPsychologyMedicine

IlluminationEngineering

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.

Xmission line132/220/400 kV

400V

~

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 areadistribution 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 areequal

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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Lesson

2

RadiationVersion 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 energycontent 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 < fred

>redX

380nm 800nm

Violet Red

f > F

violet

< violet

500 600nm Green Yellow

Fig. 2 Spectral energy Content of sun light.



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Relative LuminosityGreen

400nm

Violet

550nm 720nm

Red

Fig. 3 Luminosity Curve of Average Human

Wavelength

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

filamentsgiving 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 Incandescentlamp. 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. IncandescenceThermo 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 orElectrical 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. FluorescenceFluorescence 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 makesthe light radiated visible.

NOON

400Violet 500 600 700Red

160

120

80

40

SUN

.8

.6

.4

.2RelativeEnergy

y

Luminosit

Luminosity

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 phosphormaterial. However, the temperature of the material play a role in radiation. That is taken upnext

Color Temperature

Radiation Temperature of the materials follow Steafan Boltzmans Law:

W = kT4

.( 1 )

Absolute k

5.71x10-12

Its Boltzmans constant

or

radiation constant

Say Ambient Temperature is T0

W = k ( T4

T04

) 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

4000k

3000k

2000k

1000k

200 300 800 nm

Fig. 5 Black Body Radiation

0



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Wien displacement law

This displacement of maxima is given by wiens law, expressed as

m.T = a ( constant ) ( 3 )

k

In m 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 m

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 onethat is not transparent, does not reflect and absorbs all the energy while a Grey Body is one in

which energy radiated at each is less than that in the case of a black body. That is to say Ratio

ofVisible Energy

Total 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 selectiveradiation 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.

Thuscolor 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 forvarious natural and artificial sources is shown in Fig. 6. As may be seen color temperature, for

Blue sky it is 25000K., for a Flourescent Lamp it is 4500K., for a 500w day light it is

4000K. and for a Candle flame it is 2000K.

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

T

imeaftersunrise

1 blue and 1 daylight fluorescent lamp

orth skylight filtersAvailable to give a range from

K

ps

28 000

26 000

24 000

22 00020

Blue glass n

5,400 to 30,000

1 blue and 2 daylight fluorescent lam

000

18 000

16 000

14 000

12 000

10 000

8

1 blue and 4 daylight fluorescent lamps

Daylight fluorescent lamps

4 daylight and 1 white fluorescent lamps

000

6 000

5 500

5

3 daylight and 1 white fluorescent lamps

2 daylight and 1 white fluorescent lampsDaylight photoflood

4,500 K White fluorescent lamp

500-watt Daylight lamp

000

4

Highefficienc

yfilament

Photographi

clamps

500

4 000

3 500

Photoflash

150-watt daylight lam

CP Photo lamps - Photofloods

p

White fluorescent lamp

Gas-filled

Vacuum

3 000

2

General

Servic

e

Range of Standardfilament lamps

Heat and Drying lamps

Candle flame000

2 500

Fluorescentlampsand

variouscombinations

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 Stefans-Boltzmann Law & Wiens Law, thermoluminescence, radiationoutput is directly proportional to the operating temp.

Color temp. temp. at which complete radiator (black body) must be operated to matchthe 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 operateon the principle of incandescence, radiation output depends on operating temperature

and it gives a continuous spectrum of light while gas discharge lamps operate on theprinciple 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 operatingtemperature? Due to the fact that the radiation output is directly proportional to theoperating temp. of lamp

State principle of working of a carbon filament lamp. The ratio of the visible energy tothe 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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Lesson

3Eye and Vision I



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1. Identify similarity between eye and camera2. 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 sensitivityand 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 areresponsible 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 mentionedthat by definition 2

11 lambert is candles / m

and 21

1 ft lambert is candles / ft

Scotopic vision involving Rods takes over when brightness < 0.01 ft lambert. This vision has nocolor 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 intensityof 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 andtires 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

(Yellow

Green Hue)

Lu

minosity

Rods

ish

400 500 600 700

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 humanresources. Improving the conditions of visibility.

However, visibility depends on the Size of the object, details of the object, level or Quantity ofillumination, 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 orphysical. 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 taskslead 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

ones 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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Lesson4

Eye and Vision IIVersion 2 EE IIT, Kharagpur 2


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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 exactingthe 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 characteristicsof 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 brightnessand 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 reducedin 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 ofillumination 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

108

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 ofpupil 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 distinguishedwell. 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 & alsoshould 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 isrequired. 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 lessthan0.01 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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Lesson

5

Laws of IlluminationVersion 2 EE IIT, Kharagpur 2


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1. Define Standard of Illumination?

2. What is a Candela?

3. Understand MSLI

4. State Freschners 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 isPrimary 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

1773c 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. Packedwith Fused Thoria Powder at the bottom.

2. Supported Vertically Pure Platinum in a Fused thoria crucible with a small aperture of1.5mm 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 directionof 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 thecentre then light flux coming out through an area of 1m

2over 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 lumens, out of the sphere in Fig 2.

If the Solid Angle be d and Luminous Intensity I Cd at the center then Luminous flux in d =

d = I d lm.

d

I = Cdd

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.

= I 4 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.

Frechners law

Weber in 1830 found that I Stimulus (Intensity) produces dI Least perceptible increment

affecting sense organs. Then the ratio

dIConstant

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 Frechners Law. The same percentage changein 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

2

IE = (3)

D

Where I is

Lamberts Cosine Law of Incidence

2I cosE = (4)

D

This tells us the variation of Illuminance on arbitrary surface inclined at an angle of . Asshown in Fig 4.

Fig. 4 Lamberts 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 2

LI in direction AB Cos=

(b d )+

2 2

LI in direction AB b= 3

2(b d )+

2 2

bCos =

b + d

Illuminance at C = Illuminance at Bx Cos3

32

Illuminance at B=

2d b( )[1+ ]

Next is to measure the candle power of the lamp. Typical measurement can be done using aphotometric 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 whichis1/600,000 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 lumenflux (lm)

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

Luminous Flux = luminous intensity solid angle

Illuminance is luminous flux per unit area

Frechners Law the same percentage change in stimulus calculated from the leastamount perceptible gives the same change in sensation.

Inverse Square Law The intensity of illumination produced by a point source variesinversely as square of the distance from the source.

Lamberts Cosine Law of Incidence 2

IcosE =D

Lamberts Cosine law of Emission mI = Icos

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 outwardsfrom 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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Lesson6

PhotometryVersion 2 EE IIT, Kharagpur 2


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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. blackbody) 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 - lumens and is termed msli is the light flux incident on a task surface in lumensper 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 LaboratoryStandard. 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 testlamp 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

2

s

T s2 2

I I= I = I

S T S

2

T

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

T

Reading with Test LampI = I s

Reading with Standard Lamp(i)

2T s

1

RI = I

R(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 aopaque 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 4.

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 thinlayer 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. Seleniumand Cuprous oxide are most suitable semi-conductor materials. Steel Plate P coated with thin

layer of Selenium at 200c and annealed at 80c Producing crystalline form. It is in turn coatedby 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 therole 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 usingwall

branects. They may be portable units on pole mounted in case of street Light. In all cares weneed light distribution curves. Light distribution curves are curves giving Variation of Luminousintensity 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 showssuch 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 scaledepending on length of Radic. Then the average width of the curve DP Q R S F is msli.

Luminaire

TheyProvide 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 withinprescribed 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 lampii. to control, direct & distribute light as required

iii. to keep operating temp. within prescribed limitsiv. should beeasy to install & maintainv. 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 ofIllumination 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 thedirection 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 cant 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 outwardsfrom 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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Lesson

7

Incandescent LampsVersion 2 EE IIT, Kharagpur 2


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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 > 6000c, 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 vaporFluorescence 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 Filamentis 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, Metallizingby heating Carbon filament at high temperature in an Electric furnace efficiency improved to 4.0lm/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. In1911 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 3655K. (Osmium with a mp of

2972K & Tantalum with a mp of 3172K). Were other materials Theoretically 52 lm / W

radiation is possible at m.p but Practically, Highest radiation of 35.8 lm / W is achievable. Theyare 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. InertGases 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 withatomic 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 tightlywound 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 orType C Gas > 40 W using Inert gases

During operation Filament evaporates and Tungsten particles deposit on the interior of Bulb in aVacuum 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 forthe 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 theeffect 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 andShape of the Bulb.

The lamp is said to be most economical for the intended Service, if uniform radiation is there atstated 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 statedefficiency, 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 oftungsten & 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 anincandescent 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 highefficiency?

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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Lesson8

Discharge Lamps IVersion 2 EE IIT, Kharagpur 2


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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 HighPotential. 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 isachieved. 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 highvelocity 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 givelight of Bluish Green, deficient in red rays. In this case color rendering (CRI) improves at highPressures. 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 electrodethrough 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. Atabout 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 withSodium 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. Itneeds 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 thevisible 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 beyondincandescence.

Discharge lamps consist of discharge of electricity through a tube containing aconducting 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 timeof 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 dischargeprocess 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 currentthereafter

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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Lesson9

Discharge Lamp IIVersion 2 EE IIT, Kharagpur 2


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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 andRestaurants. They give warm white color and are often used as Blended Lamps. Low Pressure

Sodium Lamp with outer Envelopes 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 aresuitable 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 colorimproves, 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 700C with a color temperature of 2100 k at 130 lm / w efficacy.



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Table I Properties of Discharge Lamps

MERCURY SODIUMPROPERTY 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 50-1000Light 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

Separat

e orBuilt

into

Ballast

Run up timemin

Zero Zero 3 10 5

Restrike time

min

Zero Zero 5 2


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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 isaround 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 ofemission, peak emission wavelength and peak sensitivity are listed. It may be observedthat 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

TungstateBlue

white220-320 285 360-720 480

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 iscoated with Indium Oxide & that acts as an IR reflector

HP Hg-vapor Lamp gives rise to bluish white line spectrum, together with somephosphors improves color

If some luminescent powderlightRadia

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

brightnesslumen 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 onluminescent 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 hotelectrode 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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Lesson10

Discharge Lamp IIIVersion 2 EE IIT, Kharagpur 2


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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 aconstant. 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 atcathode. Further, radiation increases with the current density. At low temperatures, pressuredrops 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 100 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 WFluorescent 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 moreefficient 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. UVradiation 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 clearthat 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 lm38-91 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. Forinstant 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 visibleradiation

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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Lesson11

Illumination Systems IVersion 2 EE IIT, Kharagpur 2


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1. List Components of anIllumination 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 wh

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