electric power utilization

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



Illuminance



Inverse Square Law

5EEE F427 Electric Power Utilization and Illumination

R. Femi, EEE & I Department

Inverse Square Law



INVERSE SQUARE LAW

-Lux decreases by the square of its distance

Ep = I / d2

Inverse Square Law



Lamberts Cosine Law



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



-Illuminance not perpendicular to source

Color Temperature

10EEE F427 Electric Power Utilization and Illumination

R. Femi, EEE & I Department

Color Temperature



Color Temperature



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



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



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



"Warm white" generally means a yellow-ish type of

white, and "cool white" means a blue-ish kind of

white.

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