Phase Shift of Sinusoidally Alternating Colored Stimuli

In order to avoid luminance flicker at equal luminance of two alternating colored stimuli de Lange found that a phase shift of the stimuli with respect to each other has to be introduced.This compensation for the phase shift occurring in the retina–cortex system has been measured for a large number of wavelength combinations at a retinal illuminance of 2 trolands and a 2° field. The phase angles are approximately additive.An analysis is given in terms of more basic phase shifts between the red and green systems according to the Young–Helmholtz theory.A fixed phase-shift-vs-frequency relationship between these systems explains the phase shifts measured, although second-order nonlinear effects cause small distortions of this simple model.