A spectral compensation method for determining the flicker characteristics of the human colour mechanisms.

Abstract The modulation depth of a light of intensity I 1 , at wavelength λ 1 , and that of a light of intensity I 2 at wavelength λ 2 can be so chosen that a patch of light containing these two modulated monochromatic beams is “seen” as a steady field by one class of cones. This condition is reached if for one class of cones the increase in effective quantum catch due to an increase in I 1 , is compensated by an identical decrease in I 2 , and vice versa. Implicitly this stimulus is perceived as a modulated beam by another class of cones. The silencing of either of the two classes of cones in the red-green spectral range by this spectral compensation method resulted in similar flicker fusion curves for both the “red” and “green” cones, granted identity in respective states of adaptation. Our results show that the isolated human medium and long wavelength cone systems do not exhibit low frequency attenuation even at retinal illuminations as high as 1250 td.