Definition
The widening of the pupil of the eye, allowing more light to reach the retina. In low-light or dark conditions, the pupil dilates to increase light intake and improve vision; in bright conditions, it constricts to reduce it.
Plain English
The black circle in the center of your eye gets bigger so more light can get in. This happens automatically when it gets dark.
Context Anchor
Seen in night flying discussions when explaining how the eye adjusts after moving from bright light to darkness.
Derivation
From the Latin 'dilatare', meaning 'to make wider' or 'to spread out'. In aviation night-vision discussions, it specifically refers to the pupil widening as the eye adjusts to darkness.
Why Pilots Care
Dilation lets pilots see better in darkness; bright lights can stop or reverse it and reduce night vision safety.
Grounding Statement
When you walk from a lit hangar onto a dark ramp, your pupils begin to widen so more of the weak light reaches your eyes.
Intuition Check
Dilation does not mean the whole eye is getting bigger. In this context, it means the pupil opening is getting wider.
Example Sentence 1
After a few minutes in the darkened cockpit, pupil dilation allowed the pilot to pick out terrain features outside.
Example Sentence 2
A red flashlight was used during the preflight to avoid interrupting eye dilation for night flying.