Plain English Meaning

It's the slow process your eyes go through to start seeing properly in the dark. It takes around half an hour, and a single bright light can undo most of it in seconds.

Full Definition

The gradual physiological process by which the eyes adjust to low-light conditions, increasing their sensitivity so that objects can be seen in dim or dark environments. Full dark adaptation typically takes about 30 minutes and can be quickly destroyed by exposure to bright light.

Context Anchor

Used in night vision discussions, especially before and during night flight when a pilot is trying to preserve the ability to see outside in low light.

Derivation

From 'dark' (without light) and 'adaptation' (the act of adjusting to new conditions, from Latin 'adaptare' — to fit). Together: the eye fitting itself to function in the absence of light.