After thirty minutes in darkened conditions, the rods are 100,000 times more sensitive to light than when exposed to bright light. An example of night adaptation is walking into a dark movie theater and not being able to see objects at first, but after thirty minutes vision is much better. Bright white light in the cockpit can hinder night vision. Red light preserves night vision but interferes with colors on the charts and instruments. A panel lit with dim white light is best.
Hypoxia is a lack of oxygen in the body that prevents it from functioning properly.
Hypoxia increases with altitude, and the retina of the eye is the first organ to be affected. This can happen as low as 5,000 feet. Smoking intensifies hypoxia, as the carbon monoxide from cigarettes attaches more readily to the blood's hemoglobin than oxygen. In such a condition a pilot flying at 10,000 feet would have a physiological altitude equivalent to 15,000. Prior to a night flight, make sure all the aircraft lights are working.