Fig. 5. Modelling of the shift in spectral sensitivity induced by photoreceptor screening pigment when accumulated near the rhabdom on the basal photoreceptor R9. (A) The screening pigment, with a transmittance spectrum given by the dashed curve (compare the red reflectance spectrum in Fig. 4 and see text), acts on four different visual pigments, peaking at 530, 550, 570 and 590 nm (continuous curves). The absorption by the visual pigments (dotted curves) is obtained by multiplying the absorption spectrum of rhodopsin by the filter transmittance spectrum. (B) Normalizing the resulting spectra yields the sensitivity spectra. (C) Four different red filters (dashed curves) act on a visual pigment peaking at 570 nm (continuous curve), giving rise to absorption spectra of lower magnitude (dotted curves). (D) Normalization yields the sensitivity spectra.