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Laws of Illumination
EEE F427
Electric Power Utilization and Illumination
Illuminance
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department2
Quantity of luminous flux falling on a unit area of
surface
E = F / A , unit is lux
Inverse Square Law
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department3
Illuminance
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department4
Inverse Square Law
5EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department
Inverse Square Law
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department6
INVERSE SQUARE LAW
-Lux decreases by the square of its distance
Ep = I / d2
Inverse Square Law
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department7
Lamberts Cosine Law
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department8
Illuminance in any given point of a surface is
proportional to the cosine of the angle of incidence of
the luminous rays in the illuminated point.
Lamberts Cosine Law
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department9
-Illuminance not perpendicular to source
Color Temperature
10EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department
Color Temperature
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department11
Color Temperature
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department12
Color temperature is a measure of the light bulb's color
when illuminated, and is measured in degrees Kelvin.
The higher the number, the whiter and then bluer, the
color.
Color Temperature
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department13
Choosing the right color:
Light color is measured on a temperature scale referred to as
Kelvin (K).
Lower Kelvin numbers mean the light appears more yellow;
higher Kelvin numbers mean the light is whiter or bluer.
Most qualified bulbs are made to match the color of
incandescent bulbs at 2700-3000K.
For a whiter light, look for bulbs marked 3500-4100K.
For bluer white light, look for bulbs marked 5000-6500K
Color Temperature
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department14
Color temperatures over 5,000K are called cool
colors (bluish white), while lower color temperatures
(2,7003,000 K) are called warm colors (yellowish
white through red)
Color Temperature
EEE F427 Electric Power Utilization and Illumination
R. Femi, EEE & I Department15
"Warm white" generally means a yellow-ish type of
white, and "cool white" means a blue-ish kind of
white.