Definition
The eye's ability to see in low-light conditions, which depends on the rod cells in the retina becoming chemically adapted to darkness — a process that takes roughly 30 minutes and is reduced or delayed by prior exposure to bright light, including unfiltered sunlight during the day.
Plain English
How well your eyes can see in the dark. It takes about half an hour for your eyes to fully adjust, and bright sunlight earlier in the day can make that adjustment slower or weaker that night.
Context Anchor
Seen in night flying and night vision protection discussions, especially when considering sunglasses before flying at night.
Derivation
“Visual” comes from a Latin word meaning “to see.” “Sensitivity” comes from the idea of being able to sense or respond to something. Together, the phrase points to how strongly the eyes respond to small amounts of light at night.
Why Pilots Care
Preserving night visual sensitivity improves terrain and obstacle detection and reduces spatial disorientation risk during night operations.
Grounding Statement
If your eyes have been protected from bright light before sunset, they are usually better prepared to notice faint lights after dark.
Intuition Check
Do not assume this means simply having good eyesight. Here it means how well the eyes respond to very low light at night.
Example Sentence 1
Because he had a night cross-country planned, he wore sunglasses on the ramp all afternoon to protect his night visual sensitivity.
Example Sentence 2
Bright instrument lights in the cockpit can temporarily reduce night visual sensitivity and impair outside vision.