Color Vision
Theories of Color Vision

Three Color Theory

In 1801 the English physicist Thomas Young (1773-1829) theorized that three primary colors�namely red, green, and blue�can match all colors in hue when mixed in the proper proportions. He proposed, therefore, that there were only three basic kinds of oscillators on the retina, covering it more or less uniformly. All three oscillators would be most sensitive to light from a particular part of the spectrum. One type of oscillator would respond best to red light, another to green, and the third to blue. When light of some arbitrary mixture of wavelengths struck the retina, all three types of oscillator (or receptors) would be stimulated to some degree. The relative amount of stimulation produced in the three kinds of receptors would then determine the perceived color. This is known as Young�s trichromatic or three-color theory.

The full development of this subject was taken up nearly fifty years later by Hermann von Helmholtz, a German physicist. He elaborated upon Young�s theory and developed what is now known as the Young-Helmholtz theory. It states that there are three different classes of cones in the central retina which yield sensations of blue, green, and red from mixtures of which all other colors would presumably be perceived. The theory suggested that there is considerable overlapping so that all cones respond to almost the whole spectrum. The sum of their responses, however, will be mainly with red at one end, green in the middle, and blue at the other end.

Subsequent direct physiological measurements have found different kinds of cones with peak sensitivities at wave length of about 450 nanometers (reddish blue), 530 nm (green) and 570 nm (greennish yellow) respectively.