text: Night Operations
  ADAPTATION TO THE DARK
  J-5. Adaptation to the dark means that as darkness increases, so does visual sensitivity. Just like the
  aperture in a camera, the pupil opens to let in more light. Soldiers are unique, so they adapt to darkness at
  slightly different degrees and rates. After the first 30 minutes in the dark, visual sensitivity maxes out (to
  about 10,000 times that of normal), and it increases little after that time.
  • Visual sensitivity in the dark is affected by exposure to bright lights such as matches,
  flashlights, flares, and vehicle headlights. Full recovery from this exposure might take up to 45
  minutes.
  • Use of night vision goggles impedes dark adaptation. However, if a Soldier adapts to the dark
  before he dons the goggles, then he will adapt to the dark fully about two minutes after
  removing the goggles.
  • Color perception decreases as light decreases. Soldiers can distinguish light and dark colors
  only to the degree of reflected light intensity.
  • Darkness reduces visual acuity to one-seventh of daylight levels, so Soldiers can see only
  large objects.
  BLEACHED-OUT EFFECT
  J-6. Even when the Soldier practices off-center viewing, the image of an object that he views for more
  than two to three seconds tends to bleach out into one solid color. As a result, he can no longer see the
  object, which can increase operational risk. To overcome this effect, the Soldier must know about this
  phenomenon and avoid looking at any object for more than two or three seconds. By shifting his eyes from
  one off-center point to another, he can continue to see the object in his peripheral vision.
  SHAPE OR SILHOUETTE
  J-7. At night, Soldiers must identify objects by their shapes or silhouettes. Knowing the architectural
  designs of structures common to the AO determines the success of this technique. For example, in the US,
  a church is often characterized by a high roof and steeple, but churches elsewhere have different
  architectures.
  LIGHT SOURCES AND DISTANCES
  J-8. Table J-1 shows how far the naked eye can detect light sources at night.
  Table J-1. Light sources and distances.
  Sources Distances
  Vehicle headlight 4.0 to 8.0 kilometers
  Muzzle flash from single cannon 4.0 to 5.0 kilometers
  Muzzle flash from small-arms weapon 1.5 to 2.0 kilometers
  Bonfire 6.0 to 8.0 kilometers
  Flashlight 0.0 to 2.0 kilometers
  Lighted match 0.0 to 1.5 kilometers
  Lighted cigarette 0.5 to 0.8 kilometers
  Note: From the air, these distances can increase two to three times.