Preserving Night Vision - Colors?

one of the advantages of using colored LEDs is the claim for preserving night vision - but what colors do this?

Red - I know is traditional - and many astronomers use it.

However I have also heard about blue-green being used by the airforce in cockpits to preserve night vision -
and I would have thought this color was the opposite to red,
so is it really to preserve night vision, or is the color selected to minimize infra-red detection?.

So is it really color that preserves night vision? -
or is it a simple lack of brightness - ie: dimmness?

Any comments - spec's like wavelengths for color(s), or intensity/brightness measurements?

Thanks

If I'm not mistaken the Air Force used to use those yellow Apache finger mounted LEDs, but I haven't heard anything recently.

-Mike

Yellow 592 nm

LEDs tend to be pretty dim, so probably preserve night vision because of that.

I use an old Photon I yellow on my keyring as an EDC - it seems to work for me in preserving night vision yet the yellow seems to give my eyes good definition to see details.
Despite being fairly dim I can see enough to walk outdoors with the yellow Photon I (although the pinching is hard - I do have a Photon II to replace the Mk.I when it wears out (not!) )-
I seem to need a (much) brighter White LED light to do the same - which obviously is better for color rendition, map reading etc - but definitely interferes with my night vision.

So is any color actually "better" for preserving night vision, or is it more of a function of lack of intensity/brightness?
(or, of course, a combination of both?)

Many thanks Quickbeam - that makes a great deal of sense - and that's the argument I have seen for the green or blue-green over the traditional red (which has been called by some as a myth)

However perhaps it's just my eyes - I find it very hard to see detail under either red or turquoise (blue-green) or even green light.

I guess what I'm looking for is the best compromise between being able to make out good detail using a light at personal close distances and affecting the scotopic (night) vision the least.

Thanks.

One of the reasons that red is traditional is that hunters and military types have used them as that part of the spectrum is not visible to animals such as deer - so you do not "spook" them when you turn the light on.

Regards,

Ed

Originally posted by UnknownVT:
...looking for is the best compromise between being able to make out good detail using a light at personal close distances and affecting the scotopic (night) vision the least

Click to expand...

<font size="2" face="Verdana, Arial">Get a white Photon III and set it on its dimmest setting. If you need more light, you can always push the front button of a quick shot of brighter light.

Or...get the Eternalight with 2 Green LEDs and 2 White LEDs. Use the green on a really dim setting, then if it's not workin' for you, switch to white. You'll have the best of both worlds and can tailor your light to your needs at the time.

Eternalight with Green or Red & White option

Someone posted links to a study on CPF a few months ago performed by astronomers who wanted to know what color illumination they could use for star map reading that would allow them to perceive the faintest stars immediately thereafter. Green won, ostensibly for the reasons mentioned by Quickbeam.

Quickbeam mentions that our eyes are most sensitive to green near turquoise. The phenomena is accentuated in that our eyes are supposedly least sensitive to the red end of the spectrum and we need more than average red light energy to see anything.

Here's the posts:

Go for the green

Green or Red for Better Night Vision?

[No message]

The "Go for the green" article finishes by saying this:

A useful comparison of green light vs. red light for reading star charts in the dark can be made with a simple experiment. If you already own a red LED type flashlight, buy a green LED at Radio Shack, part no. 276-303, and replace the red LED already in your flashlight. If you also need a red LED, the RS part number is 276-310. Then try reading your star charts under both green and red light. The results should be illuminating.

So...maybe a little experiment is the best way to discover the truth ?

The reason that the militay uses blue-green for their dial-lights in aircraft and land based devices and vehicles is because night vision gear is relatively INSENSITIVE to those colors.

Typically in a night, wartime situation everyone, friend and foe will be using night vision gear, so the concept of "night adapted eyes" has to be modified a bit. Turqoise is chosen specifically because of its nearness to our most sensitive color of light. It allows the dial lights to be EXTREMELY dim, and still be readable with an unaided eye, and yet be in the zone of the spectrum where night vision gear is extremely INSENSITIVE. This provides the advantage of not giving away a ground position or aircraft cockpit.

If they were to have dial-lights and accessory lights in amber, red, or neutral, their helo cockpits and people using small led maplights would "bloom" brightly to an enemy looking at them from even an extreme distance with NV gear.

When a pilot does actually want to illuminate something brightly they will use a finger mounted low power, widely focused ir laser. This provides bright light with relatively low spill light.

If you or a friend have access to NV gear, you can demonstrate the problem caused by using red lights by having him run deep into the woods or just down a long street and light a cigarette. the burning cigarette should be EXQUSITELY bright even on gen1 gear from hundreds of feet away...

So, if you want to protect your unaided eye night vision, use red. If you want to preserve your position and not get your *** shot off, use turquoise. Also, note, a 1W or 5W luxeon will be insanely bright no matter if you have nv gear on or not...

-Daniel

OK. Here you go. It's not color, but INTENSITY of the light that affects your scotopic vision. If you want the least intense light to best preserve your night vision, it makes sense to use the light which our scotopic vision is most sensitive to, since that light could be very dim and we could still see moderately well with it. Our scotopic vision is most sensitive at almost the same wavelength as a turquoise Nichia LED (500 nm). So a dim turquoise LED would allow us to see more than a brighter LED of any other color, and yet require the least light intensity to see with and therefore preserve our night adapted vision the best.

Get a turquoise photon 2, change the 2016 batteries out for a 2032 which will very dimly light the LED, and there you have a very low intensity light that your night adapted vision will be very sensitive to.

Of course, we're talking about vision thats adapted to almost pitch blackness... Residual lighting from cities, outside lighting, etc, invalidates the use of such dim lighting.

Originally posted by Daniel Abranko:
turquoise...night vision gear is relatively INSENSITIVE to those colors.

...dial-lights in amber, red, or neutral would "bloom" brightly to an enemy with NV gear.

...to protect your unaided eye night vision, use red. If you want to preserve your position and not get your *** shot off, use turquoise. Also, note, a 1W or 5W luxeon will be insanely bright no matter if you have nv gear on or not...

-Daniel

Click to expand...

<font size="2" face="Verdana, Arial">Hmmm, much of this discussion seems to have its primary relevance to night vision gear. For a star gazer or deer hunter I'm not sure how meaningful this is.

For these non-military uses, one thing seems clear, use a dim light.

Whether it is a dim red, green or white light might depend somewhat on the usage and on the person (and their eyes).

If deer can't see red...that seems meaningful.
If star charts are best read with green...that's also meaningful.
If your eyes work only well with white (my wife seems like this)...that would be meaningful too.

In the late '80s the Navy's Health Research Center (or the Personnel Research & Development Center, can't remember which it was, they're co-located in San Diego) did a fair amount of research on this with the emphasis on preserving night vision for submarine crews and bridge watchstanders on surface ships. Their conclusion was that dim white light was the best choice for retaining night vision while being able to perform needed reading. Of course this was before the proliferation of night vision equipment in other folk's militaries worldwide.

Pat

I seem to remember reading an Air Force study years ago that concluded with something to the effect that it didn't matter anyway, as operators turn up the intensity to the point that it wrecks their night vision no matter what the color.

I've spend some time doing darkroom work, illuminated by a color safelight. (I want to say a Kodak Wratten 13 or 10, but can't remember.) It takes an average person a few minutes to adapt to that low of a light level, and I don't know of any light that wouldn't wreck it. Maybe the little fingertip lights I've read about that are supposed to be dim. An original Infinity would, as would any Arc product. At this level of light you can see objects, but they're not well defined. It's way dimmer than clear moonlight, more like overcast starlight.

The funny thing is that red LED's can be used as a safelight for color photographic paper at a level that's far brighter than the old filtered incandescent lamps were. It's the first I'd used LED's for lighting, and I believe one of the first applications for LED lighting in general.

To evaluate a red light properly for night vision, I think you need to wait until your eyes are dark-adapted, and then try the light. A red light appears much brighter after your eyes are adjusted to darkness. I suppose this is true with any light, but it's especially true with red, and a red light that seems impossibly dim might seem quite reasonable after your eyes are adjusted.

From a purely observational standpoint and without much knowledge of the known science behind human night vision, I've had some interesting experiences in the yard outside my house deep in the country (in other words, really dark at night, save for the moon and stars).

One wild experience was using a Turtlelite II 2-LED, 4AA light to go for a casual stroll at 2am. I turned the corner of an outbuilding and found a rabbit no more than 3 feet in front of me, leisurely munching on the grass! The amazing thing was that he didn't seem phased by my presence at all, even though I was shining the white LEDs right at him. It really appeared that he couldn't see in that spectrum of light! This led me to theorize that for at least some animals, what they "see" or what spooks them in human lighting is mainly IR or UV or some such spilloff, which I believe must be pretty much nonexistent with white Nichia LEDs.

Another observation is that I can use any of several LED flashlights to walk outside and get the mail, without more than perhaps 10-20% loss of night vision. Now the Turtlelite II appears relatively dim, particularly when used outdoors... but my Streamlight 4AA LED powered with lithium batteries is *much* brighter, yet still seems to preserve most of my night vision! Perhaps I'm a freak, but it seems to me that human night vision may actually depend partially on light that lies outside the usual visual spectrum, which incandescent bulbs pollute but Nichia LEDs do not.

Am I crazy?

There's a very good post -

by Steve/pneuguy
Aha -- the "light" dawns -- albeit dimly!

Also by dave/arathol
night vision
please note the follow ups when I said I wanted to see detail.

According to that "Go for the green" link above from Ikendu (which has been posted before), if you can see colors at all, your night vision is being compromised. So I think it may actually be photopic "night vision" that most people are really after.

The 2 links above this post seem to confirm this, and claim essentially that there's 2 different types of night vision. Green is supposed to be best for Photopic, red for scotopic.

Now Pat Yates says white is best! Just when I thought I had it figured out.

Red, Green, Blue-Green, or White?

from -
USAF Flight Surgeon's Guide
Chapter 8
AEROSPACE OPHTHALMOLOGY
Thomas J. Tredici, M.D.

http://wwwsam.brooks.af.mil/af/files/fsguide/HTML/Chapter_08.html

QUOTE
Cockpit Illumination: The use of red light (wavelength greater than 650 nanometers) for illumination of the cockpit is desirable, because it, like red goggles, does not affect dark adaptation. Red cockpit lighting has been traditional since World War II. The intent was to maintain the greatest rod sensitivity possible, while still providing some illumination for central foveal vision. However, red cockpit lighting did create some near vision problems for the pre-presbyopic and presbyopic aviators. With the increased use of electronic and electro-optical devices for navigation, target detection, and night vision, the importance of the pilot's visual efficiency within the cockpit has increased and new problems have been created. Low intensity, white cockpit lighting is presently used to solve those problems. It affords a more natural visual environment within the aircraft, without degrading the color of objects. Blue-green cockpit lighting is used in aircraft in which night-vision devices are used because, unlike the human eye, these devices are not sensitive to light at that end of the visual spectrum. In addition, blue-green light is the easiest for accommodative focus and is seen by the rods more readily than any other color. It is not seen as blue-green, however, but only as light. However, the enemy can easily see a blue-green light, under scotopic conditions, in any position of his peripheral field, whereas a low intensity red light would be invisible unless viewed directly.
UNQUOTE

Photopic vision is at higher levels of lighting - using mainly the cones

Scotopic vision is at dark levels - using the rods.....

BUT there is also:

QUOTE:
Mesopic Vision
There is a transition zone between photopic and scotopic vision where the level of illumination ranges from about 1 to 10-3 millilamberts. Both the rods and cones are active in this range of light, and the perception experienced is called mesopic vision. Although neither the rods nor the cones operate at peak efficiency in this range, mesopic vision may be of great importance to the military aviator, because some low level of light is usually present during night operations. Below the intensity of moonlight (10-3 millilamberts), the cones cease to function and the rods alone are responsible for vision, i.e. scotopic vision. Scotopic vision is characterized by poor acuity resolution and a lack of color discrimination, but greatly enhanced sensitivity to light.
UNQUOTE