the retina is a membrane located at the back of the eye and is made up of millions of rods and cones.
Rods
Rods are used for seeing the color grey and weak light, and they contain a fluid called rhodopsine, which helps to see at night. Each night, our rhodopsine has to be refueled, and to do that we need vitamin A. A person with a vitamin A deficiency will have trouble seeing at night.
Cones
Cones are for seeing colour and bright lights, so they don't work at night or in the dark. There are three different types of cones on our retina. Some cones see blue and purple, some see yellow and green and some see red.
Cones and rods receive the signals and then they pass through cells on the way to the brain.
above : a microscopic picture
of rods and cones