It is defined as the ratio of horizontal distance between adjacent lamps and height of their mountings.
Space-height ratio = [Horizontal distance between two adjacent lamps] / [Mounting height of lamps above working plane]
As per the principle of operation the light sources may be grouped as follows:
It is defined as the total quantity of light energy emitted per second from a luminous body.
The mean of candle power in all directions in the horizontal plane containing the source of light is termed as Mean Horizontal Candle Power.
Law of Inverse squares:
Illumination at a point is inversely proportional to square of its distance from the point source and directly proportional to the luminous intensity (CP) of the source of light in that direction.
Lambert’s cosine law:
The illumination at a point on a surface is proportional to cosine of the angle which ray makes with the normal to the normal to the surface at that point.
It is defined as the ratio of total lumens reaching the working plane to total lumens given out by the lamp
utilisation factor = [Total lumens reaching the working plane] / [Total lumens given out by the lamp]
It is defined as the number of lumens given out by the source in a unit solid angle in a given direction.
It is denoted by CP
Cp = lumens /ω
It is defined as the luminous per unit projected area of either a surface source of light or a reflecting surface and is denoted by L.
There are two types of lummer brodhun heads: