Colour discrimination in dim light: An analysis of the photoreceptor arrangement in the mothDeilephila

Summary Visual pigment absorption and spectral sensitivity are calculated for a model rhabdom based on theDeilephila rhabdom. The effect of different sky light intensity spectra on absorption and spectral sensitivity is examined, and the importance of the receptor arrangement for colour vision discussed. The quality of colour perception which can be expected for such an eye is estimated. The calculations reveal, firstly, a balance between the spectral bandwidths of rhodopsin absorption spectra and the distances between their maxima, which is of great significance with respect to colour vision. Secondly, they show that the quality of colour discrimination for dim light, at luminance levels between 0.1 and 10 cd/m², is comparable to the performance of the human eye at much higher levels of luminance.