Figure 1.
(A) Overlapping spectral sensitivities of the human photoreceptors. (B) Non-specificity of single-wavelength lights. Right panel: Pattern of photoreceptor responses to the single-wavelength light at 490 nm. (C) Principle of univariance. Right panel: Pattern of photoreceptor responses to the single-wavelength lights E1, E2, and E3 designed to elicit the same response in melanopsin. (D) Wavelength exchange between two short-wavelength lights E1 and E2 which stimulate S cones at the same level but yield different photoreceptor responses for melanopsin. Right panel: Pattern of excitations for lights E1 and E2.