Fig. 7. The absorption of sky light as a function of the angle of the incident light for different states of pupil closure for a photoreceptor with a distal rhabdomere diameter of 2 µm and one sensitizing pigment molecule per rhodopsin (R+S). The pupil adaptation is given by the pupil distance, h. (A) Photon absorption per second from a patch of blue sky of 1 square degree seen under an angle . (B) Normalization shows that the angular sensitivity function distinctly narrows upon light adaptation. The vertical lines indicate the angle of incident light that is focused on the rhabdomere border.