Luminosity and Colour

Abstract

IN conjunction with my other methods of testing colour vision, I have been using Rayleigh's apparatus for matching yellow with a mixture of spectral red and green. I find that the proportions of red and green depend upon the luminosity of the match (both the mixed colour and the simple one being of similar luminosity); for instance, I require two and a half times as much green in the mixed colour when the match is bright compared with a match at a lower luminosity. Some persons make a match which is nearly the same at several luminosities, others require more and more green as the luminosity is diminished, and others when the luminosity is diminished cannot make a match at all. So three normal sighted persons may make a similar match at one luminosity, and at another one may appear to be an anomalous trichromatic and the other colour blind. I find that a colour blind person (a dichromic with considerable shortening of the red end of the spectrum) may make a match like a normal sighted one.