Explain Light source - Pre-requisites of Colour Perception  

No colour may be detected by the eyes or by an instrument in the dark i.e.  in the absence of a light source emitting radiant energy in the visible range of the spectrum. Wrong results will be obtained if the light source is not emitting sufficient radiant energy at the critical wavelength. To avoid this, three standard illuminants i.e. light sources have been established by the International Commission of Illumination.  These are:

Illuminant A  i.e.  Incandescent lamp (2844°K)

Illuminant B i.e. noon sunlight (4000°K)

Illuminant C i.e. cloudy daylight (6800°K)