>From http://2ndbn5thmar.com/BookOne/thre-other.html - on infantry at night
For maximum dark adaptation, expose eyes to 30 to 45 minutes of darkness.
Exposure to bright light after this requires 5 to 45 minutes to regain
night vision.
...
Do not use lights or illumination. If light must be used, red filtered
light allows you to retain night vision. Blue light is more difficult for
the enemy to see, but does NOT allow you to retain night vision.
Avoid losing night vision. Close eyes against lightning, flares, headlight,
or other lights. If only one eye can be closed, that eye will maintain
night vision because it occurs independently in each eye.
Know that darkness affects visual acuity and distorts human vision.
Darkness modifies outlines, shapes, and colors. Visual sharpness is one-
seventh of what it is during the day. Shrubs look like soldiers, fences
look like enemy patrols, and a village may look like a forest.
Know that darkness affects depth perception. Height and distance are
modified. Dark objects appear farther away, light objects appear closer.
Experience can increase an observer?s ability to perceive depth. On a clear
night, you can recognize land relief up to 400 meters. At ranges less than
800 meters, Marines tend to underestimate range by as much as 25 percent.
Know that haze, smoke and fog limit night observation. Overcast clouds
limit night observation. High humidity limits night observation.
Common Errors
Fatigue. A tired set of eyes cannot see well. A tired observer is not
mentally alert. Rotate observation duty, with or without NVGs [Night Vision
Goggles], every 30 minutes.
Sleep deprivation. Sleep is needed for night observation: 5 hours per day
minimum, 6 to 8 hours per day for long-term operations. Even 10 minutes of
sleep can restore energy. Good physical fitness and stamina allows a Marine
to recover quicker.
Poor nutrition. Lack of vitamin ?A,? normally provided by eggs, cheese and
carrots, reduces night vision. U.S. forces, with good nutrition, have the
best potential night vision.
Smoking or chewing tobacco. Tobacco constricts blood vessels in the eye,
reducing night vision by up to 20 percent.
Consuming alcohol. Alcohol within 48 hours slows the ability to acquire
night vision. Alcohol impairs judgement, distance estimation, and
coordination.
...
Night vision medical problems. Some people have less night vision
capability than others. Presbyopia, the decrease in light transmission to
the retina, is common in individuals over 40 years old. Night myopia, which
affects nearsighted people, is blurred vision at night. ...An ordinary
cold, and the narcotic medicine used to treat it, decreases night vision.
Loss of night vision due to bright lights or muzzle flashes and failure to
close at least one eye.
Peace, Tom
------------------------ http://groups.yahoo.com/group/ottawa-photo-clubs
tOM A. Trottier, ICQ:57647974 http://abacurial.com
758 Albert St, Ottawa ON Canada K1R 7V8
+1 613 860-6633 fax:231-6115 N45.412 W75.714
"The moment one gives close attention to anything,
even a blade of grass, it becomes a mysterious,
awesome, indescribably magnificent world in itself --
Henry Miller, 1891-1980
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