EEE F427 - Lecture 2

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Illumination and Lights

EEE F427 - Electric Power

Utilization and Illumination

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Chapter -1 : Illumination

IntroductionDefinitions of important terms

Laws of Illumination

Types of Lamps

Electronic Control of Lamps

Lighting Schemes

Residential, Commercial lighting

Industry, flood and Street lighting.Calculux Software indoor and Area

2

EEE F427 Electric Power Utilization and Illumination

R. Femi, EEE & I Department

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Topics to be covered


R. Femi, EEE & I Department3

Define light, discuss its properties, and give the range

of wavelengths for visible spectrum.

Apply the relationship between frequencies and

wavelengths for optical waves.

Definitions and the concepts of luminous flux,

luminous intensity, illumination etc.

Solve problems

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Introduction



Human Needs

VisibilityTask Performance

Safety

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Why we use lighting

Help us find our way around, to assist visibility

Provide a safer environment

Increase the number of useful hours in the day

Help perform visual tasks, increase productivity Display objects and / or control how they appear,

improve sales

Attract attention

Improve employee working conditions

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Light Sources



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A Beginning DefinitionAll objects are emitting and

absorbing EM radiation.Consider a poker placed in a

fire.

As heating occurs, the emitted EMwaves have higher energy and

eventually become visible.3

4

2

1

Light may be defined as electromagnetic radiation that

is capable of affecting the sense of sight.

7 EEE F427 Electric Power Utilization and IlluminationR. Femi, EEE & I Department

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Electromagnetic Waves

cc

EE

BB

ElectricElectric EE

MagneticMagnetic BB

Wave Properties:1. Waves travel at the speed of

light c.

2. Perpendicular electric and

magnetic fields.3. Require no medium for

propagation.

3 x 103 x 1088 m/sm/s

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The Wavelengths of Light

The electromagnetic spectrum spreads over atremendous range of frequencies or wavelengths. The

wavelength l is related to the frequencyf:

c = fl c = 3 x 108 m/s

Those EM waves that are visible (light) have wave-

lengths that range from 0.00004 to 0.00007 cm.

Red,Red, ll

0.00007 cm0.00007 cm

Violet,Violet, ll

0.00004 cm0.00004 cm


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The EM SpectrumA wavelength of one nanometer 1

nm is:

1 nm = 1 x 10-9 m

Red 700 nm

Violet 400 nm

c = fl c = 3 x 108 m/s

1024

1023

1022

1021

10201

0191018101

71016

1015

10141013101

21011

10101

09

108

107106

105

104

Frequency wavelengthf (Hz) l ( nm)

10-7

10-6

10-4

10-3

10-1 1

10

102

103104

105

106

107

108

109

10101

0111012101

3

Gamma rays

X-rays

Infrared rays

Short Radio

waves

Broadcast Radio

Long Radio

waves

Ultraviolet

400 nm 700 nmVisible Spectrum


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Cosmic

Rays

Gamma

Rays

X-Rays UV

Infra-

Red

Micro-

Waves

TV Radio

Electric

Power

.00001 nm .001 nm 1 nm 10 nm .0001 ft.

. 01 ft.

1 ft.

100ft.

1 mi.

3100 mi.

40000 500 600 700 1000 1500

Wavelength Nanometers)

Visible Spectrum Infraredltraviolet

ABC HEAT

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The Sensitivity Curve

Wavelength l

Sens

itivity

Human eyes are notequally sensitive to

all colors.

Eyes are most sensi-tive in the mid-range

near l = 555 nm.

555 nm

400 nm400 nm 700 nm700 nm

40 W40 W 40 W40 W

YellowYellow light appears brighterlight appears brighter

to the eye than doesto the eye than does redred lightlight..

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The Sensitivity Curve



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Electrical Lighting



Electrical lighting has following advantages :

Cleanliness

Easy to control

Economical

Easy to handle

Steady output

Better reliability

Suitable for almost all purposes

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Light

Radiant energy from a hot body whichproduced the visual sensation on human eye

is called light.

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Solid Angle



The angle subtended by the partial surface area of a sphere at its

centre is called as solid angle. It is measured in steradians and

equal to the ratio of area of the surface to the square of radius of

sphere,

= area of surface/ square of radius = A/ r2 steradians

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Solid Angle

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A Solid Angle: Steradians

Working with luminous flux requires the use of

a solid angle measure called the steradian (sr).

AR

The Steradian

2

A

RW

A solid angle of one steradian(1 sr) is subtended at the

center of a sphere by an area

A equal to the square of its

radius (R2

).

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ISOTROPIC SOURCE

Theoretical source which radiates all itselectromagnetic energy equally in all directions.

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Four terms are used to describe light

Luminous Flux (lumen)

Luminous Intensity (candela)

Illuminance (lux)

Luminance (candela/m2)

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Luminous Flux

The total quantity of radiant energy per secondresponsible for visual sensation from a

luminous body is called Luminous Flux.

It is represented as F (or) and measured in

lumens.

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Luminous Flux

Luminous flux is the portion of total radiant power that is

capable of affecting the sense of sight..

Typically only about 10% ofthe flux emitted from a light

bulb falls in the visible

region.

The unit for luminous flux is the lumen

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Lumen

It is the unit of luminous flux. One

lumen is defined as the luminous

flux emitted per unit solid anglefrom a point source of one candle

power.

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Lumens = candle power * solid angle

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Luminous Flux (Lumen)

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Luminous Intensity

The luminous intensityI for a light source is the luminousflux per unit solid angle.

WW FI

W

Luminous intensity:

FI

W

Unit is the candela (cd)

A source having an intensity of one candela

emits a flux of one lumen per steradian.


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Candle power (CP)

Candle power is the light radiating capacity of a sourcein a given direction and is defined as the number of

lumens given out by the source in a unit solid angle in

a given direction.

Candle Power = Lumens / solid angle

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Candela

It is the unit of luminous intensity. It is defined as 1/60thof the luminous intensity per cm2 of a black body

radiator at the temperature of solidification of

platinum.

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Luminous flux for Isotropic Source

An isotropic source emits in all

directions; i.e., over a solidangle of 4 steradians.

Luminous flux: F = 4I

W = 4pW = 4p srsr

Thus, for such

a source, theintensity is: 4

F F

I

W

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Illumination of a Surface

The illuminationEof a surfaceA is defined as the luminousflux per unit area (F/A) in lumens per square meter which is

renamed a lux (lx).

Unit: lux (lx)F

EA

An illumination of one lux

occurs when a flux of one

lumen falls on an area of

one square meter.WW

RR

AreaAreaAA

Illumination,Illumination, EE

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Illuminance (E)



Quantity of luminous flux falling on a unit area of surface

E = F / A , unit is lux (lumens/m2 or meter candle)

Summer noon, under a cloudless sky 100 000 lux

Ditto, but in the shade 10 000 lux

In the open under a heavily-overcast sky 5000 lux

Artificial light, in a well-lit office 1000 lux

Artificial light, average living-room 100lux

Street lighting 5-30 lux

Full moon, on a clear night 0,25 lux

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Lux or Metre Candle

It is the unit of illumination and is defined as the luminous

flux falling per square meter on the surface which is every

where perpendicular to the rays of light from a source of

one candle power and one meter away from it.

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Foot-Candle

It is unit of illumination and is defined as the luminousflux falling per square foot on the surface which is

every where perpendicular to the rays of light from a

source of one candle power and one foot away from it.

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Illuminance

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Luminance ( candles/m2 )



Amount of light reflected back from the surface andreaching the eye.

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Important Terms

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Lamp Efficacy



Luminous Efficacy or efficiency

- measure of a lamps efficiency

-Ratio of the luminous flux to the electrical

power consumed

-- Unit is in lm/W

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Luminous (lamp) Efficacy

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Candle Power

Mean Spherical Candle PowerIt is defined as the mean of candle powers in all

directions in all planes from source of light.

Mean Hemi Spherical Candle Power

It is defined as the mean of candle in all directionsabove or below the horizontal plane passing through thesource of light.

Mean Horizontal Candle Power

It is defined as the mean of candle powers in alldirections in horizontal plane containing the source oflight.

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Important terms

Specific ConsumptionIt is defined as the ratio of the input to the average candle power.

Glare

It is defined as the brightness within the field of vision of such a

character as to cause annoyance, dis-comfort, interference withvision or eye fatigue.

Space Height Ratio

It is defined as the ratio of horizontal distance between adjacent

lamps and height of their mountings

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Important terms

Utilization Factor or Coefficient of UtilizationIt is defined as the ratio of total lumens reaching the

working plane to total lumens given out by the lamp.

Maintenance Factor

The ratio of illumination under normal working

conditions to the illumination when the things are perfectly

clean is known as maintenance factor.

Depreciation FactorIt is defined as the ratio of initial meter-candles to the

ultimate maintained meter-candles on the working plane.

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Important terms

Waste Light Factor:Whenever a surface is illuminated by a number of sources of

light, there is always a certain amount of waste of light onaccount of overlapping and falling of light outside the edges ofthe surface. (1.2 for rectangular area, 1.5 for irregular area)

Absorption Factor:

The ratio of total lumens available after absorption to thetotal lumens emitted by the source of light is called the absorptionfactor.(unity for clean atmosphere and 0.5 for foundries)

Beam Factor:The ratio of lumens in the beam of a projector to the lumens

given out by lamps is called Beam Factor(0.3-0.6)

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Important terms

Reflection FactorThe ratio of reflected light to the incident light is called

the reflection factor.

Solid Angle

It is angle generated by the line passing through the point

in space and the periphery of the area.it is denoted by W.

Steradian

It is the unit of solid angle and is defined as the solidangle that subtends a surface on the sphere equivalent to the

square of the Radius.


EEE F427 - Lecture 2

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