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Originally Posted by Cdre Gibs
Red light is used to prevent night vision loss and to reduce the chance of being spotted.
But you may ask yourself, why red light, why not say Blue or Green. Well the simple fact is that red light is at the bottom of the visable light spectrum just befor it become infrared. Now infrared as every 1 knows is a light we cant see, we can feel it tho (called heat), but we cant see it. So if your using a visable light source thats damn close to a light source we cant see, what do you think happens. Our pupils expand of course to gather as much of this nearly none visable light into the retina so as our feeble brains can process it.
Blue light believe it or not is actualy the closest colour light to white light, so its of course no good, Green follows not to far behind.
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Close.
Rhodopsin is the main pigment in the rods of your retina. Rods are designed to absorb low-level (low lux) light, but at a very poor resolution. Rhodopsin is purple, so it reflects mostly red and blue, and absorbs green most efficiently.
Years ago, this much retinal biochemistry was unknown. Emperical data showed that green required the least lux for a given resolving ability, with red and blue following. Red filters and lenses were more economical to make, and red is generally absorbed more efficiently by the majority of substances on our planet (namely water and chlorophyll), so red propagates less than blue or green.
However, we have since learned that it takes far less green light power, and our eyes have greater resolving power with green light, that most low-light operations have started using it. Night-vision goggles, backlit LCD displays, cockpits.
Red is still used on vehicles because of the propagation factor. Water in the atomsphere absorbs it very quickly; far more quickly than green or blue. Blue and violet are the last light waves to be filtered out in the deep ocean (violet extends to nearly 50 meters depth).