Absorption of white light in photoreceptors.
The fraction F of incident light absorbed by a photoreceptor of length l has traditionally been given by F = 1 - e-kl, where k is the absorption coefficient of the photoreceptor. Unfortunately, this widely-used expression is incorrect for absorption of the type of light most common in natural scenes--broad spectrum "white" light--and significantly over-estimates absorption. This is because the measured values of k are only valid at the absorbance peak wavelength of rhodopsin, whereas at other wavelengths (which the eye may also see) k is lower. We have accounted for the wavelength dependence of k and calculated the absorption of white light from four different natural radiant sources: the quantal irradiances of natural daylight and a patch of very blue sky, and the quantal reflections of soil and green foliage irradiated by natural daylight. Based on these results, a simple averaged correction for white light stimulation is derived, F = kl/(2.3 + kl), which is valid for a wide range of k and l, and therefore applicable to both vertebrate and invertebrate photoreceptors.
Warrant
E J
EJ
Department of Zoology, University of Lund, Sweden. eric.warrant@zool.lu.se
Nilsson
D E
DE
D000818:Animals; D008027:Light; D008433:Mathematics; D010786:Photoreceptor Cells / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology; D012168:Retinal Pigments / Q000502:physiology; D013053:Spectrophotometry
D012168:Retinal Pigments