Giles Brindley has conducted important work on the physiology of vision. By studying the way that colour matches break down under very strong illumination, he was able to deduce for the first time the spectral sensitivity of the visual pigments in the cones, and estimate the density of the red-sensitive pigment, its photosensitivity and its rate of regeneration. Amongst other work, he has made important contributions to the analysis of the electroretinogram, the (subjective) electric phosphene and the nature of afterimages.