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DARK ADAPTATION Going suddenly from bright light into darkness is a common occurrence.In such cases, the recovery of a previous maximum level of dark adaptation can take from 5 to 45 minutes in continued darkness.c. Dark adaptation for optimum night visual acuity approaches its maximum level in about 30 to 45 minutes under minimal light conditions.Vision with I2 devices is primarily photopic, but the low light levels produced by I2 devices do not fully bleach out rhodopsin.Brief flashes from a white (xenon) strobe light, commonly found on aircraft, have little effect on night vision because the pulses of energy are so short.If a previously dark-adapted crew member wearing an I2 device removes the device in a darkened environment, a 30-minute dark adaptation level can be regained in about two to three minutes.On the other hand, exposure to a flare, a searchlight beam, or lightning may seriously impair night vision.a. Dark adaptation is the process by which the eyes increase their sensitivity to low levels of illumination.d. Night vision devices affect dark adaptation.

DARK ADAPTATION
Going suddenly from bright light into darkness is a common occurrence. For example, people experience this when they enter a movie theater during the day or leave a brightly lit room at night. At first they see very little, if anything. After several minutes, they can see dim forms and large outlines. As time goes by, more details of the environment become apparent as further dark adaptation occurs.
a. Dark adaptation is the process by which the eyes increase their sensitivity to low levels of illumination. Individuals dark-adapt to varying degrees and at different rates. During the first 30 minutes, the sensitivity of the eye increases roughly ten-thousandfold. Very little increase in sensitivity occurs after that time.
b. The lower the starting level of illumination, the more rapid complete dark adaptation is achieved. For example, less time is required to dark-adapt completely after leaving a darkened theater than after leaving a brightly lit hangar.
c. Dark adaptation for optimum night visual acuity approaches its maximum level in about 30 to 45 minutes under minimal light conditions. If the dark-adapted eye is exposed to a bright light, the sensitivity of that eye is temporarily impaired. The amount of impairment depends on the intensity and duration of the exposure. Brief flashes from a white (xenon) strobe light, commonly found on aircraft, have little effect on night vision because the pulses of energy are so short. On the other hand, exposure to a flare, a searchlight beam, or lightning may seriously impair night vision. In such cases, the recovery of a previous maximum level of dark adaptation can take from 5 to 45 minutes in continued darkness.
d. Night vision devices affect dark adaptation. If a previously dark-adapted crew member wearing an I2 device removes the device in a darkened environment, a 30-minute dark adaptation level can be regained in about two to three minutes. No dark adaptation period is necessary before using the I2 device. Vision with I2 devices is primarily photopic, but the low light levels produced by I2 devices do not fully bleach out rhodopsin. Use of the device does not seriously degrade dark adaptation.