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Thread: Preserving Night Vision - Colors?

  1. #1

    Default 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

  2. #2
    Flashaholic* Xrunner's Avatar
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    Default Re: Preserving Night Vision - Colors?

    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

  3. #3

    Default Re: Preserving Night Vision - Colors?

    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?)

  4. #4

    Default Re: Preserving Night Vision - Colors?

    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.

  5. #5
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    Default Re: Preserving Night Vision - Colors?

    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

  6. #6

    Default Re: Preserving Night Vision - Colors?

    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
    <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

  7. #7
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    Default Re: Preserving Night Vision - Colors?

    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.

  8. #8

    Default Re: Preserving Night Vision - Colors?


  9. #9
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    Default Re: Preserving Night Vision - Colors?


  10. #10

    Default Re: Preserving Night Vision - Colors?

    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 [img]images/icons/smile.gif[/img] ?

  11. #11

    Default Re: Preserving Night Vision - Colors?

    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 ass 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

  12. #12
    Flashaholic* Quickbeam's Avatar
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    Default Re: Preserving Night Vision - Colors?

    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.

  13. #13

    Default Re: Preserving Night Vision - Colors?

    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 ass 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
    <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.

  14. #14
    Pat Yates
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    Default Re: Preserving Night Vision - Colors?

    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

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    Default Re: Preserving Night Vision - Colors?

    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.

  16. #16
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    Default Re: Preserving Night Vision - Colors?

    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.

  17. #17
    Flashaholic* milkyspit's Avatar
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    Default Re: Preserving Night Vision - Colors?

    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?

  18. #18

    Default Re: Preserving Night Vision - Colors?

    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.

  19. #19
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    Default Re: Preserving Night Vision - Colors?

    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. [img]images/icons/mad.gif[/img] [img]images/icons/smile.gif[/img] [img]images/icons/grin.gif[/img]

  20. #20

    Default Re: Preserving Night Vision - Colors?

    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...hapter_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

  21. #21
    *Flashaholic* McGizmo's Avatar
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    Default Re: Preserving Night Vision - Colors?

    From personal observation and experience, it seems to me that certain considerations beyond color are equally significant if not more important. I don't know the correct terms but hopefully can communicate my thoughts coherently.

    For starters, night vision to me means the ability to see in the night or dark environments. Typically there is an ambient level of light that one becomes adjusted to. I have no idea at what level of this ambient light your vision goes from photopic to scotopic. I do know that my ability to see is effected by the level of contrast present. By this, I am referring to the range in intensity of light from the bright areas to the shadows. A good level of moisture in the air or fog greatly reduces the contrast level as the ambient light is mixed and dispersed.

    Once acclimated, with the ambient light, I can see and distinguish items to some extent but may find that I need to add illumination to an area in shadow to a higher level of recognition or add light to some object for more detail recognition. Ideally, one would have an adjustable light that could slowly be increased to the extent necessary and not beyond. Whether there is an advantage to the specific color of this light probably depends on the aspects described above. More important to me than color would be the ability to dial up the intensity of the light versus switching on a light source at a fixed level. Also very significant, in my opinion is the type of beam used. Ideally it would be a flood pattern with a consistant density of light throughout if the area to be illuminated is close at hand. The beam should be a spot beam if the target is further away. Obviously the key is to add to ambient just enough to accomplish the task of recognition. If the light source is so bright or of an inappropriate beam pattern such that a hot spot of reflected light is returned to your eyes, your night vision has been compromised.

    I have had a fair amount of experience with the Nichia white LED's and feel fairly confident that white light can be effectively used for needed illumination without adverse effect on ones night vision. The key is in adding light to the environment in small increments. It may well be that monochromatic light sources allow for a more sloppy approach or over supply of needed light with less detrimental results. From what I can glean from the information above as well as what I have read elsewhere, the optimal color choice is likely a function of the ambient level of light present.

    I for one have no idea when I am functioning in photopic or scotopic mode and suspect that in the uncontrolled environments that I frequent, I am going from one mode to the other as ambient changes. The cockpit of a plane is a more controlled environment than the one I'm likely to find myself needing illumination in. For me, I'm happy to settle for white light but I would certainly like the ability to control its intensity as well as dispersion.

    In the future, I hope to be able to procure a flashlight that doesn't currently exist. It has a single point source of light that can be electronically varied from 1 lumen of output to 100 lumens. It also has a multi element adjustable lens that can be focused from a 2 degree beam to a 70 degree beam. The dang thing will probably cost $750 but I will gladly sell all of my other flashlights to more than cover this expense! [img]images/icons/grin.gif[/img] Did I mention it was waterproof and titanium? [img]images/icons/grin.gif[/img]

    - Don

  22. #22

    Default Re: Preserving Night Vision - Colors?

    Originally posted by McGizmo:
    From personal observation and experience
    <font size="2" face="Verdana, Arial">Excellent post Don.

    I am fast becoming more convinced that for me it is a matter of intensity (or lack of) that helps me preserve the ability to see better in dim environments.

    Most of the time when I need a light I want to see detail/read - but I want to be able to switch that light off and recover as quickly as possible for my level of dark adaption -

    So it appears that perhaps a dim white light is needed for me - preferably adjustable level going from off and increasing illumination until it is just adequate for the purpose.

    Because of all the talk about colors - I have had for a long time a yellow Photon - which seems a fairly good compromise (for me) - as the color still gives pretty good definition and may actually enhance contrast (even on map reading, the only real loss is the yellow populous areas - but I can figure these out) but probably because it is generally dim.

    The yellow Photon has worked for me - but I often wondered whether this was just "wishful thinking" on my part - I had tried traditional red but found that definition was not good for me - and I would need a really bright red light - which seems to affect my dark adaption more than a dimmer yellow.

    The problem I see for blue-green or green is that our eyes are very sensitive to this wavelength - so the ability to adjust intensity/brightness levels is vital - as over-exposure brightness will affect the eyes more.

    In my minimal research on this topic I have come across the Rigel Systems lights for Astronomers with adjustable brightness (it has been covered on this forum before) -
    with this interesting page:
    http://members.cox.net/rigelsys/why_red.html

    Here are the flashlights:
    http://members.cox.net/rigelsys/flashlight.html
    and
    http://www.airydisk.com/starlite.htm

  23. #23
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    Default Re: Preserving Night Vision - Colors?

    Originally posted by UnknownVT:
    [QBScotopic vision is characterized by poor acuity resolution and a lack of color discrimination, but greatly enhanced sensitivity to light.
    UNQUOTE[/QB]
    <font size="2" face="Verdana, Arial">That was exactly the way stuff looked in the darkroom...fuzy/ill-defined. I'd always thought it was just my weak vision.

  24. #24

    Default Re: Preserving Night Vision - Colors?

    UnknownVT...thanks for the posts on the Starlite and Skylite. I hadn't seen them before! Pretty cool!

  25. #25

    Default Re: Preserving Night Vision - Colors?

    Originally posted by Daniel Abranko:
    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.
    &lt;snip&gt; -Daniel
    <font size="2" face="Verdana, Arial">The helicopters around here used to want a lot of light to land. They've switched to night vision and want very little red and blue are a huge problem and they say use green if you have to use anything. I'm thinking of trying some of the glow powder to see how they like that.

  26. #26
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    Default Re: Preserving Night Vision - Colors?

    Originally posted by Mike Painter:
    [QBThe helicopters around here used to want a lot of light to land. They've switched to night vision and want very little red and blue are a huge problem and they say use green if you have to use anything. I'm thinking of trying some of the glow powder to see how they like that.[/QB]
    <font size="2" face="Verdana, Arial">Hmmm...you've just given me an idea: Green trail markers. Little green LED lights, dim enough not to screw with night vision equipment, bright enough to see with the naked eye. Sounds pretty simple, plus this gives me something to do tonight. Let me know if you want me to post the results.

  27. #27
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    Default Re: Preserving Night Vision - Colors?

    One of the options I'm including in the BTx torch is a dim mode (AOM), primarily designed so that you can locate your torch in total darkness. The preferred colour for most of my happy customers is cyan. Lighting up a cyan LED at fractions of a milliamp will give enough light to see larger obstacles in a totally dark environment. The only place to test such theories is deep in the unpopulated mountainous regions of Wales or Scotland. Many of our country's towns and cities are changing from SOX (low pressure sodium bulbs) to SON-T (High pressure sodium bulbs) for streetlighting and consequently background light pollution prevents any useful testing to be done with dim mode lighting. Around here you ned to use a torch that is bright to light up the near ground as it is silhouetted against a pinkey yellow glow in the sky. The extra ambient light actually makes it more diffiocult to negotiate your way down a nearby unlit footpath or track without some serious torchware!
    At Nant Gwynnant where I do all my serious torch testing I can illuminate effectively with a single LED orange torch as effectively as I can with a 4 or 5 LED torch back home in the light polluted midlands!
    Maybe they should consider using cyan luxeons as streetlamps in areas where light pollution is highly undesirable!

  28. #28

    Default Re: Preserving Night Vision - Colors?

    Good inputs -

    The problem I see (pun intended) for green or blue-green is that our eyes are most sensitive in those wavelengths (green for photopic and blue-green for scotopic) so the intensity level is much more critical not to affect our dark adaption when one switches off the light.

    Red makes more sense - because scotopic vision is insensitive to red, while photopic can use red - so at the right (low) levels only the photopic vision is affected leaving the scotopic vision still at full sensitivity.

    However as others have also mentioned red light does not give such good definition - and the only way to get better definition is to increase the level of intensity - which eventually defeats the dark adaption.

    I note that EMPOWERTORCH uses orange - perhaps, like me, this may be a good compromise color/wavelength to still see good definition at low intensity levels, but affects dark adaption least when the light is switched off?
    (I actually use a Photon 1 yellow)

  29. #29
    Flashaholic* Quickbeam's Avatar
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    Default Re: Preserving Night Vision - Colors?

    Some great information about preserving night vision on that Starlight flashlight site.

    Synopsis: Night vision is the result of the buildup of rhodopsin (commonly called "visual purple"). This takes 30 to 60 minutes in complete darkness. DIM red light has no effect on rhodopsin. Any other color at an intensity where you can see the color (not just identify it as "light") destroys it and it has to build up again. Hence why dim red light is best for preserving night vision. Green light is used by the military for night vision equipment which is less sensitive to green light. However green light will break down rhodopsin-based night vision instantly at an intensity where the color of the light is recognizable.

    This makes sense IMHO as to why red light seems to be better at preserving your night vision.

  30. #30
    *Flashaholic* McGizmo's Avatar
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    Default Re: Preserving Night Vision - Colors?

    Doug,

    This makes sense to me as well and echos what I learned about vision in school many years ago. However, in the real world and outside, the ambient level of light comes into play and I don't know at what level the ambient itself will destroy the rhodopsin. Will a full moon take you to this point? So maybe the hot ticket would be a dimmable or varying illumination white LED source with a removable red filter? A red filter over a white LED is ineficient anyway since thare is little red light in the LED's white light. This way if it's really dark, you can use the red filter. If ambient or light polution takes you past the rhodopsin level, then you could use the white light at a level just adequite to suit your needs. If color distinction is required, you would want the white source available anyway... Sounds like the new small Eternalight with one red LED and 2 white might fit the bill nicely.

    Incidentally, growing up there was the common "myth" that eating carrots improved your vision. In school it was explained that carrots provided the body with materials needed for the production of rhodopsin.

    - Don

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