Plain English Meaning
The chemical in the back of the eye that lets you see in the dark. Bright light uses it up, and it takes time to build back up before your night vision works well again.
Full Definition
A light-sensitive pigment found in the rod cells of the retina that enables vision in low-light conditions. Rhodopsin is bleached (broken down) by bright light and must regenerate over time to restore night vision sensitivity.
Context Anchor
Seen in instrument flying and night flying discussions about the eyes, night vision, and adjusting to darkness before flight.
Derivation
From Greek 'rhodon' meaning rose and 'opsis' meaning sight or vision -- literally 'rose-coloured vision pigment,' named for its reddish-purple colour. Knowing it is a pigment that bright light destroys helps explain why night vision recovers slowly.