When light energy hits the retina, the retinal changes from a cis to a trans configuration.
Step-by-step explanation:
The retina contains an essential chromoprotein, rhodopsin, that is very crucial in turning a light signal to an electric signal. The rhodopsin comprises of 11-cis-retinaldehyde that gets transferred into all-trans-retinaldehyde as soon as light hits the retina. This change in configuration generates electrical signals that are further travelled by the optic nerve of the eye.
Also, this change in configuration of rhodopsin, causes bleaching due to which vision is created.