The spectral shape of A2 visual pigments

A mathematical description is proposed for the shape of absorption spectra of A2 visual pigments in which the shape continuously varies with peak wavelength lambdamax. The description consists of two parts: (a) the peak and short wavelength region is described by the sum of three lognormal curves and (b) the long wavelength region is derived from an existing physical model, including temperature dependence. The resulting function can be used as a basis for action spectra, also if a large long wavelength tail is present. The parameters of the functions as a function of lambdamax were assessed by fitting experimental goldfish rod and cone spectra. By interpolation of these parameters spectra can be calculated for lambdamax values all over the visual spectrum.