Common unit of light intensity is candela. It is Luminous intensity in the Perpendicular direction of a surface, 1 / 600,000 of a black body at temperature of solidification or Freezing of Platinum under Standard Atmospheric pressure. It is abbreviated as Cd. It is indicative of Light Radiating Capacity of a source of Lamp.

Measurements may be made on Illumination meter or Lux meter also in this instead of the screen adjust the meter to get the same reading on photometric bench. Fig.2. shows a method where distance is varied to get the same reading on the meter.