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8/10/2019 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
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Topics to be covered
EEE F427 Electric Power Utilization and Illumination
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
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department4
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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EEE F427 Electric Power Utilization and Illumination
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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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EEE F427 Electric Power Utilization and Illumination
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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
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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
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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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EEE F427 Electric Power Utilization and Illumination
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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)
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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 )
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Amount of light reflected back from the surface andreaching the eye.
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Important Terms
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Lamp Efficacy
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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 Electric Power Utilization and Illumination