Short-wavelength-sensitive cones do not contribute to mesopic luminosity

Abstract

It has been suggested that the short-wavelength-sensitive cones (S cones) play a significant role in the transition from scotopic to photopic vision (the Purkinje shift). We address this issue directly over a 5-log10-unit range of light levels covering scotopic, mesopic, and photopic vision. At each light level we make flicker matches to two reference stimuli by 2-Hz flicker photometry. The two reference lights (441 and 481 nm) differ only in their stimulation of S This novel technique utilizes the different magnitudes of the rod and cone Stiles--Crawford effects. Despite the large difference in S-cone stimulation by the two reference lights (more than 1 log10 unit), the pairs of luminosity functions are indistinguishable at each light level tested. The results indicate that S cones do not contribute to either photopic or mesopic luminosity.