Molecular biology of photoreceptor spectral sensitivity

Abstract

The wavelengths of spectral sensitivities of the visual systems of animals extend from about 300 nm in the near ultraviolet to above 800 nm in the far red. Some species utilize almost this entire spectral range, whereas others are restricted to narrower ranges within these broad limits (Bowmaker, 1991a). The spectral range of ‘visible’ light is limited by two factors. First, because of the filtering effects of the atmosphere, most (about 80%) of the spectral radiation at the earth’s surface is restricted to wavelengths between about 300 and 1100 nm with the energy distribution having a maximum at about 480 nm and the quantum distribution maximal at about 555 nm. Secondly, the quantal energy of photons above about 850 nm is too low to lead to photoisomerization of organic molecules, whereas photons below about 300 nm have sufficiently high energies to be destructive to proteins (see Knowles and Dartnall, 1977).