A theory of colour vision

At the beginning of the 19th century, the mechanisms behind human colour vision were unknown. In the year 1801, Thomas Young, an English doctor, proposed the theory that the eye was capable of perceiving light in three colours, using three types of colour receptors on the retina.

in 1856, the German scientist Hermann von Helmholtz made some refinements to Young's theory, and Johannes von Kries carried out some work which led him to identify the cone structures in the eye. The theory assumed that these three kinds of receptors ('cones') had different sensitivities to different wavelengths of light, approximately corresponding to the colours red, green or blue. However, other than some experiments using colour matching, nothing further was established until the early 1960s, when the retinal receptors ('cones') were finally identified.

At that time, the researcher George Wald discovered by experiment that the three different kinds of cone absorbed light near 445, 535, and 565 nanometers, hence were sensitive to light in the basic primary colours. When these signals are sent to the brain, the appropriate colour is 'seen'. When combined signals are sent, either white, or secondary colours are 'seen' in the visual cortex.

One of the biggest strengths of this theory is that is can explain several kinds of colour blindness, as the failure or malfunction of one or more types of cone, producing a reduction in the perception of colours. This theory does not fully explain some aspects of vision, however. Some elements, including afterimages, red-green and yellow-blue colourblindness, are best explained by the opponent-process theory.

spare aardvark says re trichromatic theory: The three wavelengths you mention are not primaries in the usual way that's understood: they're at violet, blue-green, and green.

Encyclopædia Britannica

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