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Old April 25, 2009, 12:48 AM   #4
Chindo18Z
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Join Date: July 23, 1999
Posts: 493
SPUSCG: Red lights don't help you see better in the dark...they prevent whatever natural level of night vision your eyes already possess from degrading. This is because red light's wavelength does not destroy your natural night vision (as white light will). Red light saves the natural night vision you were born with (which, in humans, is not that great). We have to wear $8000 night vision goggles to see as well as a cat (or an owl) in the dark.

Try an experiment. Next time you are out in the dark (or in a dark room or closet), notice how long it takes for your natural night vision to come on board. Initially, going from a lit area into total darkness, everything appears black. After a few minutes, you notice that you can see features previously hidden in the shadows. This is because your eyes begin to generate a chemical compound called visual purple as soon as they enter a dark situation. You've been doing this naturally every day of your entire life, but most folks don't think about it.

This is why, when you turn out the lights in your bedroom, the room appears extremely dark, but (if you are still awake 20 minutes later) you can then see most things in the room.

From Wikipedia:

"Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. Because they are more light sensitive, rods are responsible for night vision. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. There are about 120 million rod cells in the human retina.

Rhodopsin, also known as visual purple, is a pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light, enabling vision in low-light conditions. Exposed to light, the pigment immediately photobleaches, and it takes about 30 minutes to regenerate fully in humans.

Rhodopsin of the rods most strongly absorbs green-blue light and therefore appears reddish-purple, which is why it is also called "visual purple". It is responsible for monochromatic vision in the dark.

Experiments by George Wald and others showed that rods are most sensitive to wavelengths of light around 498 nm (green-blue), and are completely insensitive to wavelengths longer than about 640 nm (red). This fact is responsible for the Purkinje effect, in which blue colors appear more intense relative to reds at twilight, when rods take over as the cells responsible for vision."


In layman's terms:

White light instantaneously destroys the visual purple in the rods at the rear of your eye. This chemical is your body's natural mechanism for seeing in the dark. Your daily biological production of this chemical compound is related to our day/night solar cycle. Your eyes normally begin to produce visual purple as it gets dark (dusk). Animals (and humans) aren't set up by nature to deal with bright lights in the dark of night (fire, tactical lights, car headlights, etc.). Once your eyes are hit by a bright light in the dark, you are temporarily blinded. Once the light goes away (and after a few minutes of gradual visual purple regeneration), your previous night vision begins to return.

This explains why everything appears darker at night when you first walk outside from a well lit interior...or why a Surefire tactical light can blind an opponent in the dark...and why it is difficult to see into the dark woods much beyond the white light range of a campfire you are standing near.

Your eyes are set up to see either color/day OR monochromatic/night and need 15-30 minutes to make a gradual transition.

Red light wavelength does not destroy visual purple. This makes red lensed light sources useful at night for reading maps and instruments or for use in signalling. Its also why the taillights of the car in front of at night are red (not white). You'd otherwise be somewhat blinded by the driver in front of you.

In the military today, flashlight lenses and the instrument lights in cockpits and crew compartments tend to be blue-green. This is due to red light washing out certain printed red/brown featues on military maps as well as blue-green being easier to look at with night vision goggles.

Red light allows you to read, search, or navigate without blinding yourself.

On the other hand, running around with a continuously "on" red light mounted to your safety goggles, ballcap, or helmet is...well...running around with a bright red "shoot me" light attached to your head.

Your friends are just using red lights to avoid tripping over things or to find things. However, they are making themselves well-defined targets for their opponents.

For home defense, a small red or blue flashlight or headlamp would be useful for seeing something that you need to do (unlock a door, find a magazine you dropped, dial 911, check out an injury, etc.). Just don't turn it on unless you absolutely need it (if you are trying to remain hidden). If you really need light, flip a light switch on...

Hope this helps...
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Last edited by Chindo18Z; April 25, 2009 at 09:34 AM.
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