rod

one of the two types of light-sensitive cell present in the RETINA of the EYE . The rods enable vision in dim light because of a PIGMENT called rhodopsin (visual purple). This pigment degenerates or bleaches when light is present and regenerates during darkness. In bright light all the pigment bleaches and the rods cannot function. Bleaching of the pigment gives rise to NERVE IMPULSES that are sent to the brain and interpreted.