Rod cell
A light-sensing cell in the retina that works in dim light and does not detect colour.
Also: rods
Rods are the eye's night-vision cells. They far outnumber cones and are much more sensitive, able to respond to very faint light, but there is only one kind, so they cannot tell colours apart. In moonlight we see with rods, and the world looks grey. Rods respond best to blue-green light and poorly to red. As evening falls, red flowers darken first while blue ones seem to glow, an effect named after the Czech scientist Jan Purkinje. Rods take many minutes to reach full sensitivity in the dark.