Under certain conditions, studies on visual thresholds as a function of luminance have indicated that the transition from cone to rod function occurs within a narrow range of luminances. This has suggested the possibility of establishing a “rod luminance scale” for lower intensities. Based on standard photopic and scotopic luminosity data, a correction curve for translating from cone to rod luminance specification has been calculated. This curve emphasizes the factors involved, but when applied to empirical data leaves residual discrepancies between rod functions determined at different wavelengths. An empirical determination of correction factors permits rectification of the luminance scale, except for a narrow transition region for each wavelength.
C. S. BRIDGMAN, "The Correction of Low Intensity Luminance Functions for the Purkinje Effect," J. Opt. Soc. Am. 42, 832-836 (1952)