How Do Our Eyes Adjust to the Dark?
Quick Answer
In darkness the pupils widen and the retina's light-sensitive rod cells rebuild a pigment called rhodopsin, greatly boosting night vision over about 20 to 40 minutes.
The Full Story
When you enter a dark room, the pupil dilates within seconds to let in more light. The bigger change happens in the retina, where cone cells (for colour) adapt within about 10 minutes. Rod cells, which are far more sensitive but see no colour, regenerate their light-sensitive pigment rhodopsin more slowly. Full dark adaptation takes around 20 to 40 minutes and can make the eye many thousands of times more sensitive. A bright light bleaches rhodopsin instantly, which is why a torch can ruin your night vision.
Key Facts
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"Why pilots and astronomers use red lights at night."