Dark Adaptation or Night Vision Adaptation
Dark adaptation is the process by which the eyes adapt for optimal night visual acuity under conditions of low ambient illumination. The eyes require about 30 to 45 minutes to fully adapt to minimal lighting conditions. The lower the starting level of illumination, the more rapidly complete dark adaptation is achieved. To minimize the time necessary to achieve complete dark adaptation and to maintain it, you should:
- avoid inhaling carbon monoxide from smoking or exhaust fumes;
- get enough Vitamin A in your diet;
- adjust instrument and cockpit lighting to the lowest level possible;
- avoid prolonged exposure to bright lights;
- use supplemental oxygen when flying at night above 5,000 ft (MSL).
If dark-adapted eyes are exposed to a bright light source (searchlights, landing lights, flares, etc.) for a period in excess of 1 second, night vision is temporarily impaired. Exposure to aircraft anti-collision lights does not impair night vision adaptation because the intermittent flashes have a very short duration (less than 1 second).
Scanning the sky for other aircraft is a very important factor in avoiding midair collisions, and it should cover all areas of the sky visible from the cockpit. Most of us are instinctively alert for potential head-on ncounters with another aircraft. Actually, a study of 50 midair collisions revealed that only 8% were head-on. However, 42% were collisions between aircraft heading in the same direction. So, compared with opposite-direction traffic, your chances of having a midair are over 5 times greater with an aircraft you are overtaking or one that is overtaking you. It is necessary for you to develop and practice a technique that allows the efficient scanning of the surrounding airspace and the monitoring of cockpit instrumentation as well. You can accomplish this by performing a series of short, regularly spaced eye movements that bring successive areas of the sky into the central (foveal) visual field. To scan effectively, scan from right to left or left to right. Begin scanning at the top of the visual field in front of you and then move your eyes inward toward the bottom. Use a stop-turn-stop type eye motion. The duration of each stop should be at least 1 second but not longer than 2 to 3 seconds. To see and identify objects under conditions of low ambient illumination, avoid looking directly at an object for more than 2 to 3 seconds (because it will bleach out). Instead, use the off-center viewing that consists of searching movements of the eyes (10 degrees above, below, or to either side) to locate an object, and small eye movements to keep the object in sight. By switching your eyes from one off-center point to another every 2 to 3 seconds, you will continue to detect the object in the peripheral field of vision. The reason for using off-center viewing has to do with the location of rods in the periphery of the retina for night or low-intensity night vision (peripheral), and their absence in the center of the retina (fovea). Pilots should practice this off-center scanning technique to improve safety during night flights. Some wonder whether it is a good idea or not to wear their Randolph aviator sunglasses
at night, and given what we have learned here it is clear that pilots should NOT wear any sunglasses at night! Tomorrow I will have the 3rd part in this series on vision and we will discuss why it is not prudent to wear aviator sunglasses
when flying an airplane at night. In the meantime, please be sure and leave comments below. Until next time keep your wings straight and level Hersch! JetAviator7 There is no sport equal to that which aviators enjoy while being carried through the air on great white wings. — Wilbur Wright, 1905
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