The colorimetric properties of the spectrum

Abstract Those properties of the eye which determine its behaviour in the measurement of luminous intensity and colour are completely defined by two sets of numerical data which express, as functions of wave-length, its behaviour to monochromatic radiation throughout the visible spectrum in respect of these two aspects of the visual effect of a stimulus. The first of these functions is embodied in the “ Relative Visibility ”* curve of the spectrum, and the second is embodied in a curve showing the locus of the spectrum on the “ colour triangle ” of some trichromatic system. These two functions may be combined to give the “ mixture curves ” of the spectrum, by means of which we can calculate both the photometric and colorimetric values of any stimulus from its spectral energy distribution. The nature and significance of these various functions are sufficiently well understood to need no explanation here.