# Red light for preserving night vision?



## gcbryan (Sep 29, 2011)

Red light is often used to preserve night vision. Since we have three areas of our eye (cones) that react to light (red, green, blue) is night vision preserved when you use green or blue light or only red?

I was looking at a response curve for each of those colors and it seemed that green was the most responsive, red next, and blue the least.

Why wouldn't blue be better for preserving night vision or conversely why wouldn't green be better since we are more responsive to it?

Thanks in advance to anyone who has the answers!


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## Burgess (Sep 29, 2011)

There are some Excellent and informative threads here, on this very topic.



Seek, and ye' shall Find.



_


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## JacobJones (Sep 29, 2011)

Night vision can be preserved with any colour light as long as it is dim enough to not activate the cones, this is knows as scotopic vision, only the rods are active and they don't see colour, you will be seeing in black and white no matter what colour the light you use is. This topic crops up very often and if you look around there are more in depth versions of what I have just explained


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## dreamlayers (Sep 30, 2011)

Rod cells (used for night vision) have their peak sensitivity between green and blue, and they're sensitive to both green and blue. Sensitivity falls off toward red, and they're almost totally insensitive to red. Here's a sensitivity graph from Wikipedia and another graph which shows colour corresponding to wavelength.


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## LEDAdd1ct (Oct 1, 2011)

There is actually a night vision forum, and in that forum, a sticky, and in that sticky, one particular post I think nails it. I highly recommend you consult the thread:

Link


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## Burgess (Oct 1, 2011)

Thank you for posting that very old Link !


Still very informative, and makes very interesting reading !


Can't imagine why it is *Closed* however.


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## gcbryan (Oct 1, 2011)

OK, after all the reading, here is the short version for anyone else who is wondering the same thing (I read all of the threads here and elsewhere).

Red is the only color which will actually preserve night vision (as in essentially no negative effect). That is to define night vision as involving only the rods and making note that red is the only color that the rods aren't sensitive to.

If you use any color or white at a low enough level then you can minimize the impact on your dark adaptation. White light is just as good as cyan or any other color in this regard. It minimizes the impact but it still affects the rods since they are sensitive to any light other than red.

If you are looking for a color that is efficient (seems bright to your eyes at a minimum setting) then cyan is a good choice since rods are very sensitive to this color. However, this has nothing to do with dark adaptation. White would work just as well for that purpose. At this point it's just a personal choice. Maybe it enhances contrast in your environment or whatever.

Using a red light will not affect the rods. However you should still use it at a lower level or there will be a short period of adjustment for your cones after you go back to the darker environment. This is due to shocking the cones with too much light. There may be after images that take 5 minutes or so to fade if you use any light including red on too high a level. This is a short lived thing however. Dark adaptation of the rods on the other hand can take 30 minutes to an hour or more.

The bottom line is if what you are really talking about is true night adaptation then red is the best solution to that problem. Anything else is a lesser solution.

It seems that many people discussing this issue aren't actually talking about night adaptation but rather about what color light they prefer to use when they are using a light at night.

If you need dark adapted eyes which means using the rods (flying an airplane VFR at night) and you need color or reading ability (reading the cockpit instruments) which means using the cones then red will cause the least problems for you.

If you don't need to switch between these two extremes then you either don't need a light in the first place or you need one all the time and dark adaptation is not so much of an issue for you and therefore whatever color of light you use has nothing to do with this issue. Moderation is your lighting is all you might need.


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