Night vision is a physical process that takes time and is easy to ruin. Here is what the FAA says about dark adaptation, the night blind spot and protecting your eyes.
The rods, which do most night seeing, can take approximately 30 minutes to fully adapt to darkness, and a bright light can completely destroy that adaptation. At night the center of your vision has a blind spot, so look about 10 degrees off center of what you want to see and scan slowly.
Once fully adapted, the rods are estimated to be 10,000 times more sensitive to light than the cones. Because cones are concentrated near the fovea, there is a night blind spot in the center of the field of vision, which is why objects seen straight on seem to dim or vanish (FAA-H-8083-25C, ch. 17). Keep light discipline: the FAA advises neutral density (N-15) sunglasses in bright sunlight before a night flight to speed dark adaptation, low lighting so light does not monopolize night vision, and a dim white flashlight for maps and checklists, never shone in anyone’s eyes.
The handbook describes manned aircraft, but the eyes are the same eyes at the control station. Staring has its own trap: a stationary light stared at for a prolonged time in the dark may appear to move, an illusion called autokinesis (FAA-H-8083-25C, ch. 17). Off-center scanning technique and the daytime method are on our scanning page, and the night operating rules are on our 107.29 page.
Sources: FAA-H-8083-25C, ch. 17, Night Blind Spot · FAA-H-8083-25C, ch. 17, Dark Adaptation · FAA-H-8083-25C, ch. 17, Night Vision Protection · FAA-H-8083-25C, ch. 17, Autokinesis
FAA-H-8083-25C, ch. 17, Dark Adaptation
The rods can take approximately 30 minutes to fully adapt to darkness. A bright light, however, can completely destroy night adaptation, leaving night vision severely compromised while the adaptation process is repeated.
FAA-H-8083-25C, ch. 17, Night Vision
Off-center viewing is another type of scan that pilots can use during night flying. It is a technique that requires an object be viewed by looking 10° above, below, or to either side of the object.
FAA-H-8083-25C, ch. 17, Sunglasses
pilots and crew members should wear neutral density (N-15) sunglasses or equivalent filter lenses when exposed to bright sunlight. This precaution increases the rate of dark adaptation at night and improves night visual sensitivity.
FAA-H-8083-25C, ch. 17, Autokinesis
When flying in the dark, a stationary light may appear to move if it is stared at for a prolonged period of time.
Sources: FAA-H-8083-25C, ch. 17, Dark Adaptation · FAA-H-8083-25C, ch. 17, Night Vision · FAA-H-8083-25C, ch. 17, Sunglasses · FAA-H-8083-25C, ch. 17, Autokinesis
Similar to the FAA test, not the actual test questions. Each answer shows its FAA source.
Question 1 of 3
FAA source: FAA-H-8083-25C ch. 17, Aeromedical Factors, Night Vision Illusions, Autokinesis
Question 2 of 3
FAA source: FAA-H-8083-25C ch. 17, Aeromedical Factors, Night Vision, Scanning Techniques
Question 3 of 3
FAA source: FAA-H-8083-25C ch. 17, Aeromedical Factors, Night Vision, Scanning Techniques
At night the cones in the center lose much of their sensitivity and the rods become more sensitive, so the ability to see an object in the center of the visual field is reduced. Looking slightly off center helps compensate.
Source: FAA-H-8083-25C, ch. 17, Night Blind Spot
It is the illusion that a stationary light moves when stared at for a prolonged time in the dark.
Source: FAA-H-8083-25C, ch. 17
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More on this topic: Part 107 operations and decision-making.