In human color vision each incident spectral energy distribution is coded in three values, corresponding to the responses of the red, green, and blue receptor systems. The Stiles-Crawford effect and the color phenomena associated with it indicate that these three values are in a different degree for each wavelength dependent on eccentricity of the point of entry of the light in the pupil.
A rather quantitative description of the facts is given by a theory in which leak factor of the light to the surrounding tissue in the outer and the inner segment is involved. The leak factor implies that for oblique light the effective pathway in the outer segment is shortened. This results in narrowing of the fundamental response curve of the particular receptor.
Theory strongly points to rather high densities of the photopigment in the receptor, but not improbably high. On the contrary, there is agreement with other sound suggestions and estimates of the density value. As absorption curves for the red, green, and blue pigments we used Pitt’s curves. The agreement of different experimental data with this theory strongly supports the Young-Helmholtz hypothesis, as far as the receptor layer is concerned, and also indicates that the curves derived by Pitt are fairly good approximations of the absorption curves of the photopigments after correction for absorption of light by the ocular media.
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