Abstract

We used HMP¹ to establish isoluminance for 667-nm, R, and 550-nm, G, counterphase flickering lights in thirty-eight university males. In HMP, R and G are presented in a series of fixed luminance ratios (R/G) and modulation. M. is reduced to the flicker threshold. Plots of log 1/M vs log R/G are V-shaped. Isoluminance is determined by using a model to estimate the location of the V with respect to the log R/G axis. The model requires that M depend on the sensitivity to luminance contrast S and that S depend on the observer’s limiting Weber fraction C_w, and the mean luminance L of each stimulus: S = 1^q/(C_w). We initially assumed linearity (q = 1.0). Goodness of fit was highly variable but improved significantly if q was allowed to vary (0.2 ≤ q ≤ 1.0). We also examined the assumption that C_w is invariant with chromaticity by holding the mean luminance constant across R/G in two experienced observers. That assumption proved true for R/G less than the isoluminance point but not for greater values of R/G.

© 1991 Optical Society of America