Researchers have found that the melanopsin pigment in the eye is potentially more sensitive to light than its more famous counterpart, rhodopsin, the pigment that allows for night vision. In this illustration, computer models of human melanopsin (violet) and squid rhodopsin (green) are superimposed. Similar to visual pigments, melanopsin provides the interface between the physical world, responsible for light detection, and the physiological world of brain signaling. Melanopsin mediates a process termed "photoentrainment," which takes in light to set the clock of "circadian rhythms." These rhythms (often termed the body clock) represent the biological implementation of the 24-hour day/night and optimize the corresponding physiology.