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I went on a night flight tonight after not flying for a few months. I didn't have any monochrome lights, so I actually just covered a flashlight of mine with red athletic tape (which acted as a filter really well).

I know that using monochrome is the most important thing about preserving night vision - but does it particularly matter, while flying, which color I use?

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You will want to use red light.

Why?

See Does red light preserve your night vision? on the Biology StackExchange for a good explanation of the biology and physiology involved, and how it relates to perceptual ability.

As stated in this answer (by leonardo) to that question:

If one is exposed to red light (above ~650 nm), it would activate the L-type cones mainly (possibly some M-type activation), but no rod activation. Rods are the low light receptor cells in our eyes, and as such, are very sensitive to the photon density, or brightness, entering the eye.

This is just my speculation, but I think it's plausible that if you were in a completely dark environment with just a red light, filtering out the higher frequencies, night vision could be spared in the sense that we don't activate the rod cells.

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  • $\begingroup$ Thanks! I guess I'll keep it below 650. Cree has a few colored LED options - their Amber-595nm, Red/Orange-620nm and the Red-630. Does this mean using the Amber will preserve night vision better than the others? $\endgroup$
    – Keegan
    Commented Dec 15, 2014 at 17:00
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    $\begingroup$ Note that you'll probably need a plain white flashlight anyway -- as abelenky points out red is a lousy light for color discrimination (charts and gauges should be illuminated with a light that lets you see colors). Red/White LED flashlights are easy to find (I personally like bicycle headlamps for this purpose since you can usually dim the white light). $\endgroup$
    – voretaq7
    Commented Dec 15, 2014 at 17:30
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    $\begingroup$ @SpongeBob: Higher frequencies are shorter wavelengths, so 595nm is a higher frequency than 630nm. The important thing to note is that activating rods (about 600nm and shorter) causes the rhodopsin in your eyes to bleach (which means you lose your night vision). Since the cones do not help you see detail, they are not useful for things like reading instruments or maps. So you want to minimize your rod exposure while maximizing your cone exposure. Your eye has more red cones than any other color, so using red light makes the most sense. $\endgroup$
    – Gabe
    Commented Dec 15, 2014 at 17:55
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    $\begingroup$ @SpongeBob If you believe that your edit is accurate, you really should make it on the original answer as well. Right now the quote disagrees with the original. Personally I find your edit confusing; "above X frequency" is equal to "shorter than Y wavelength" where for appropriate units Y=c/X, and as you reduce the wavelength of visible light, you go from red (at the long wavelength end of the spectrum) to blue and ultimately violet (at the short wavelength end). So saying "above 461 THz" is very different from saying "above 650 nm". Light is also commonly discussed in terms of wavelength. $\endgroup$
    – user
    Commented Dec 16, 2014 at 8:41
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    $\begingroup$ @SpongeBob Your edit is wrong. "Above 650nm" is both the correct phrasing and the logical unit (nm) to use. "Above" means higher, longer, or greater -> in the direction of infrared if we are talking about wavelength. By changing the unit to frequency, "above" now still means higher, but this instead means faster -> in the direction of shorter wavelength or towards blue and UV. Also, as a scientist and engineer who has worked with optics and visible light for many years, never have I seen anyone use THz as a working unit. Frequency is popular in some EM ranges, but not this one. $\endgroup$
    – J...
    Commented Dec 16, 2014 at 9:56
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I know everyone is going to say you need a red light, and that should be your primary light. But I think its important to also have a white light and one other color (typically green).

The reason is simply that red light makes everything look red, and makes it hard to distinguish colors! Can you actually verify that the AVgas is light blue when you look at it under a red light? Can you see bright red, important items on a checklist? Reading red-text against a white background can be very difficult with a red light. On a VFR map, airport symbols are blue or magenta to indicate towered/untowered airports, but they both look the same under a red light.

So while your primary light should probably be red, you'll need alternate colors and plain-old white for many things.

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    $\begingroup$ There are some headlamps available on the cheap that allow you to switch between red and white light as needed. And they're hands-free too. $\endgroup$
    – Tim
    Commented Dec 15, 2014 at 18:17

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