light adaptation

n. The process of becoming accustomed to ambient light levels so as to maximize perception at that level of illumination. This normally includes controlling the amount of light entering the pupil by widening when light level is low and narrowing the opening when there are higher light levels, depletion of light-receptive chemicals in the retinal rods and cones, and processes of reciprocal inhibition in the retinal nerve cells. In very low levels of illumination it also includes using edges of the retina rather than the center as the edges contain mostly rods, which are more light sensitive than are the cones, which are concentrated in the center of the eye.