After six to seven minutes the eyes are 100 times more sensitive than when you entered the dark. Full adaptation takes 30 minutes, at which time the rods of the eye are 100,000 time more sensitive. This is due to the buildup of a photosensitive chemical called visual purple , the key to night vision. Although it takes 30 minutes for dark adaptation to occur, it can be lost in a second or two of exposure to bright light. Minimize the use of white light in the cockpit and keep it as dim as possible.
Dark adaptation is an independent process in each eye.
If you are exposed t light, close one eye to preserve half your dark adaptation. The cones of the eye, used for day vision, provide peripheral vision. Night vision uses rods. This creates a blind spot in the center of the eye at night. If you detect something with peripheral vision, the natural tendency is to turn and look directly at it.