Light is portion of the electromagnetic spectrum . The visible section of the spectrum extends from 400-700nm (nanometres, 1nm = 1 × 10 -9 metres). Within this range the human vision system can detect this radiation and convert it into information. The wavelength corresponds to the way the vision system is stimulated, as the wavelength changes so does the response of the vision system. We equate the wavelength to colour.

The human vision system is a complex imaging system of which the eyes only make up a part. The visual stimulus received via the eyes is processed in various sections of the brain. The retina of the eye contains four different types of receptor. However, it is generally believed that colour information is coded by the retinal and post-retinal neural structures as just three types of signals that are often called ‘channels’.

The channels roughly separate the various wavelengths into regions that correspond to blue (400-500nm), green (500-600nm) and red (600-700nm).