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By Bob Amick
Although the ideal night hike can be conducted with light from the moon or "scatter" light (light reflected off clouds or direct illumination from cities if you are close to one); some nights are just too dark for the eyes to accommodate. One of the techniques that used to be recommended and seems to work well is to utilize the peripheral vision by looking from side to side in a sweeping pattern. Peripheral vision is provided by the rod cells of the retina which are far more sensitive to low-intensity light but are only able to interpret images in a "gray-scale" without color.
Color vision works well in brighter light and is registered by the. cone cells in the fovea near the center of the retina which are sensitive to color but less sensitive to low-level light.
One of the advantages of using flashlights with red filters is that red light does not "bleach" the visual purple of the retina. White light of flashlights, or other colors in the yellow, green, blue spectrum bleaches the visual purple causing temporary insensitivity to low light levels. It usually takes five minutes or longer for the visual purple to regenerate to a point where night vision is restored. This is one of the reasons that military aircraft, naval vessels, command centers, etc., use red lights to maintain night vision.
Sometimes it's fun for Scouts to try "night vision" military/law enforcement light amplification glasses if available. (they are a bit "pricey" but sometimes can be borrowed).
Bob Amick, Explorer Advisor, High Adventure Explorer Post 72, Boulder, CO
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