A system of photometry and colorimetry based on cone excitations

A system of photometry and colorimetry is proposed that is based upon cone action spectra. Instead of X, Y, Z tristimulus values, the new system divides the visual stimulus into L, M , and S components, which are related to the relative excitation levels of the three classes of human cone photoreceptors (long‐wavelength‐sensitive L , middle‐wavelength‐sensitive M , and short‐wavelength‐sensitive S). On the assumption that luminance is proportional to L + M , with S cones making no contribution to it, a chromaticity diagram results in which the relation between chromaticity coordinates and cone excitations is transparent, rather than inadvertently obscured as in the CIE system.