Flicker photometry as a function of retinal illuminance

Abstract

We measured spectral sensitivity for wavelengths 500–700 nm by heterochromatic flicker photometry (HFP) to a 570-nm standard light. We also measured spectral sensitivity for the same wavelengths using a flickering light on a 570-nm background. The alternation rate 16 Hz for both protocols. The parameter was the retinal illuminance of the 570-nm standard in the HFP protocol and the 570-nm background in the flicker sensitivity protocol. Retinal illuminance varied over a three-log unit range from 1.6 to 500 td in half-log unit steps. We then fit the HFP spectral sensitivity data at each retinal illuminance by an additive combination of Smith-Pokorny fundamentals. The flicker sensitivity data were treated in the same way. From these functions we could derive the relative change in LWS/MWS components for HFP as a function of retinal illuminance. The HFP functions showed a decrease in LWS/MWS as retinal illuminance increased, similar to reported data. From the flicker sensitivity data, we could also derive the amount of LWS and MWS components as function of background retinal illuminance. These could be plotted as a threshold-vs-radiance function and traced out a Weber function.