ILLUMINATION

ILLUMINATION:

Light is the prime factor in the human life as all activities of human beings ultimately depend upon light. 

Artificial lighting produced electrically, on account of it's cleanliness, ease of control, reliability, steady o/p, as well as its low cost, is playing an important role in everyday life.

Illumination differs from light very much,though these terms are used more or less.
Light is the cause and illumination is the result of that light on surfaces on which it falls.

Terms used in illumination:

1. Light is defined as the radiant energy from a hot body which produces visual sensation upon the human eye. It expressed  in lumen-hours.

2. Luminous flux is defined as the total quantity of light energy is emitted per second from luminous body & measured in lumens (or) cd-sr .

3. Luminous intensity in any given direction luminous flux emitted by the source per unit angle and measured in the direction in which intensity is required. Measured in candela (cd) or lumens per steridian.

4. Lumen is the unit of luminous flux & is defined as the amount of luminous flux given out in space required by one unit of solid angle by a source having an intensity of one candle power in all directions & the total lumens given out by source of one candela is 4-pie lumens.

5. Candle power is the light radiant source in a given direction & is defined as the number of lumens given out by a source of one unit solid angle in a given direction.

6. Illumination is defined as the luminous flux (number of lumens),falling on the surface per unit area. It is measured in lumens/meter square or lux or metre candle.

7. Candela is the unit of luminous intensity & is defined as the 1/60th of the luminous intensity per centimeter square of a black body radiator at the temperature of solidification of platinum(2,043 K).

8. Mean spherical candle power(MSCP) is defined as the mean of candle powers in all directions & in all planes from the source of light.

9. Lamp efficiency is defined as the ratio of luminous flux to the power input & expressed in lumens per watt.

10. Specific consumption is defined as the ratio of the power input to the average candle power & is expressed in watt per candela.

11. Brightness or luminance is as the luminous intensity per unit projected area either a surface source of light or a reflecting surface. It is measured in nit (candelas/meter square). Bigger unit of luminance is stild (candelas/centimeter square).