Regeneration of rhodopsin or the purplish pigment in the dark is called
The rod cells of eye contain a purplish pigment called visual purple, or rhodopsin. Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. Bright light splits rhodopsin and in the dark, it needs to be resynthesized. However, it takes some time for rhodopsin to form again. This process of resynthesis is called dark adaptation. This is the reason why on entering a dark room, you experience difficulty in seeing objects for a while.