Photorecepors : The receptor cells of eye which are light sensitive and have the photo-pigments are called photoreceptors or visual cells.

They are of two types 1. rod cells 2. cone cells.

1. Rod cells : The rod cells contain a purplish pigment called rhodopsin. They funcion in dim light and at night. They are responsible for the Scotopic vision. 

Bleaching : Bright light splits rhodopsin into a scotopsin and a carotenoid pigment retinene or retinal and this process is called bleaching. 

Dark adaptation : In the dark, rhodopsin is resynthesized from scotopsin and retinal. This process is called “dark adaptation.” It makes the rods functional.

2. Cone cells : The cones have a pigment called iodopsin. They function in daylight and artificial bright light produces images and give colour vision.

The cone cells conain three different wavelength.One pigment (erythrolabe) is sensitive o red light another (chlorolabe) to green and the third (cyanolabe) to blue.