A system of mesopic photometry

Nearly all the studies to develop mesopic luminous efficiency functions employ brightness matching. Brightness matching elicits parvocellular-channel response, which does not follow Abney's law of additivity as required by photometry. A reaction-time methodology appears to isolate magnocellular-channel response, which seems to be additive. In this study, a set of mesopic luminous efficiency functions were obtained using a novel psychophysical method, which measured reaction time differences between the two eyes. The luminous efficiency functions are well described by a simple model that linearly combines the spectral sensitivities of rods and cones. Based on this model, a preliminary system of mesopic photometry was defined and adapted for practical use.