Why is red light used for night vision? Why not yellow or other colours of light?
In: Technology
While I don’t know the biological reason why, the colour red doesn’t compromise your own night vision. After your eyes have adjusted to the dark you don’t tend to recoil from the light, cover your eyes, re-adjust to the light etc when the light that gets turned on is red.
So if you need someone to move between looking at some kind of screen and then immediately being in a dark place (eg: outside at night), or vice versa, that screen should be red to take advantage of this effect.
Red light is used to help prevent loss of night vision because there are less red receptors in the human eye. Only the red receptors lose their sensitivity, leaving the green and blue receptors unaffected and retaining their dark sensitivity.
However, it has since been found that the levels of light affect night vision more than colour. That’s why aircraft cockpits don’t use red light in the dark as it makes little difference in practice.
Night vision takes about 10 minutes to develop and the best way of keeping it working is to cover one eye while working in light, uncovering it when back in the dark again.
By night vision do you mean infrared? If so, colour here is a representation of the amount of heat being given off by an object, and the reason red is used for ‘cold’ colours is because radiating heat is basically just light that’s *more red* than visible red light – ie, infrared – so it makes sense to the human brain to display infrared light as red light when shifting it into the visible spectrum.
if you don’t mean infrared then I suspect your premise must be wrong because non-infrared night vision is displayed with a green hue, not a red one.
Your rods rely on rhodopsin, and your cones rely on photopsin. The longer you spend in the dark, the more of these chemicals end up in your eyes, and the more sensitive your eyes become. Exposure to light photobleaches these chemicals. That’s why adjusting to a bright environment happens very fast, but adjusting to a dark one takes much longer.
Your rods are what you mostly use for night vision. Red light does not photobleach rhodopsin, so your rods remain sensitive.
How useful this is compared to just having a really dim yellowish light, I’m not sure. I have a flashlight with a “firefly” mode that I use if I wake up in the middle of the night and need to move around the house.
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