Theory of Color Vision

Helmholtz performed his work on vision between 1853 and 1868 at the Universities of Konigsberg, Bonn, and Heidelberg, and he published his results in the three-volume Handbook of Physiological Optics (1856–1866). Many years before Helmholtz’s birth, Thomas Young (1773–1829), a distinguished scholar with accom- plishments ranging from physics to Egyptology, had proposed a theory of color vision very similar to Helmholtz’s. Helmholtz changed Young’s theory slightly and buttressed it with experimental evi- dence. The theory we present here has come to be called the Young–Helmholtz theory of color vision (or the trichromatic theory).

In 1672 Newton had shown that if white sun- light was passed through a prism, it emerged as a band of colored lights with red on one end of the band, then orange, yellow, green, blue, indigo, and, finally, violet. The prism separated the various wave- lengths that together were experienced as white. Early speculation was that a different wavelength corresponded to each color and that different color experiences resulted from experiencing dif- ferent wavelengths. However, Newton himself saw difficulties with this explanation. When he mixed various wavelengths, it became clear to him that the property of color was not in the wavelengths themselves but in the observer. For example, white is experienced either if all wavelengths of the spec- trum are present or if wavelengths corresponding to the colors red and blue-green are combined. Similarly, a person cannot distinguish the sensation of orange caused by the single wavelength corre- sponding to orange from the sensation of orange caused by mixing red and yellow. The question was how to account for the lack of correspondence between the physical stimuli present and the sensa- tions they cause.