# Preserving Night Vision - Colors?



## UnknownVT (Dec 31, 2002)

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


----------



## Xrunner (Dec 31, 2002)

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


----------



## UnknownVT (Dec 31, 2002)

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?)


----------



## UnknownVT (Dec 31, 2002)

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.


----------



## edmoses (Dec 31, 2002)

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


----------



## ikendu (Dec 31, 2002)

> 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


----------



## lemlux (Dec 31, 2002)

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.


----------



## ikendu (Dec 31, 2002)

Here's the posts:

Go for the green 

Green or Red for Better Night Vision?


----------



## Lux Luthor (Dec 31, 2002)

[No message]


----------



## ikendu (Dec 31, 2002)

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




?


----------



## Daniel Abranko (Dec 31, 2002)

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


----------



## Quickbeam (Jan 1, 2003)

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.


----------



## ikendu (Jan 1, 2003)

> 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.
> ...


<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.


----------



## Pat Yates (Jan 1, 2003)

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


----------



## Albany Tom (Jan 1, 2003)

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.


----------



## RAH (Jan 1, 2003)

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.


----------



## milkyspit (Jan 2, 2003)

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?


----------



## UnknownVT (Jan 2, 2003)

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.


----------



## Lux Luthor (Jan 2, 2003)

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.


----------



## UnknownVT (Jan 3, 2003)

*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


----------



## McGizmo (Jan 3, 2003)

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!




Did I mention it was waterproof and titanium?





- Don


----------



## UnknownVT (Jan 3, 2003)

> 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


----------



## Albany Tom (Jan 3, 2003)

> 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.


----------



## ikendu (Jan 3, 2003)

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


----------



## Mike Painter (Jan 3, 2003)

> 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.
> <snip> -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.


----------



## Albany Tom (Jan 4, 2003)

> 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.


----------



## EMPOWERTORCH (Jan 5, 2003)

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!


----------



## UnknownVT (Jan 5, 2003)

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)


----------



## Quickbeam (Jan 8, 2003)

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.


----------



## McGizmo (Jan 8, 2003)

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


----------



## UnknownVT (Jan 8, 2003)

Is yellow light a combination of red and green wavelengths?

Perhaps that's why yellow/amber works for me and some others.

I find that monochromatic red does not give me enough definition - ie: I find a dim pure red very hard to see by - eg: I probably would not choose a red light to walk by. 

I do understand that scotopic vision (the "true" night vision) is least disturbed by red as it is pretty insensitive to that wavelength - 

But probably for me I want a light that's good enough to see clearly by, but disturbs my dark adaption the least when I switch the light off 
(I suspect it's not true/pure scotopic vision I am using - but perhaps the in-between mesopic vision that uses both rods and cones in the eye?).

So perhaps yellow works because it is a combination of red which is cone (photopic) sensitive, but does not affect scotopic rods, with the addition of some eye sensitive green wavelength - to help illuminate objects - but disturbs dark adpation minimally when switched off...

Is this what I've managed to inadvertantly chance upon, without much more than just usage and what seems to work for me? 

Does that make any sense?


----------



## Quickbeam (Jan 9, 2003)

Possible reason why our eyes like amber and turquoise monochromatic light better than others: 



> Is yellow light a combination of red and green wavelengths?


<font size="2" face="Verdana, Arial">It can be, or it can be produced in a monochromatic manner. 

Our eyes work by detecting only 3 colors - Red Green and Blue. Our brain combines the quantity of detection of those colors in adjacent cones to allow us to see the full spectrum. If I were to shine a Red and Green light of the right intensity onto a white target, the light reflected back into our eyes would be interpreted as "Yellow" (try it with a red and green LED light - overlap the edges of the beams and you should see a patch of yellow). Now if I shine a light that only produces the wavelength of yellow light on a target (like a yellow LED), our brain would also consider that "Yellow".

So a yellow LED is just that, not a combination of green and red light. One wavelength only, detected partially by the red cones and partially by the green cones.

(Lightbulb goes on over head!) - This may be why you get better resolution with the yellow light. Think of a monitor, which uses tiny red, green and blue phosphors on the screen to make all the colors we see. If you project red onto the monitor screen, only 1 of 3 pixels is lit. If you project yellow, 2 of 3 pixels are lit, thereby increasing the resolution of the picture (2/3 instead of 1/3 of the screen is active, allowing for twice the detail.) Perhaps this is what is happening on the retina - 2 of the 3 cones in each cluster is active thereby increasing the resolution of the observed object!

AND we should expect the same effect from monochromatic Turquoise light (Blue and Green cone activation) and - if it existed - monochromatic Magenta (blue and red cone activation)!

This does seem to account for the observations of many people that Amber and Turquoise light feels "better" on the eyes than the other monochromatic colors - because you're using 2 of 3 cones in each cluster to see with (instead of just 1 cone) and thereby doubling your resolution and detail of the objects you are looking at.

WOW! Havn't had an epiphany in a long time. That felt good! And all this before my first cup of coffee!


----------



## Blikbok (Jan 9, 2003)

I have read both Doug Kniffen's report and the one at Equipped.org. One caveat: some astronomy charts are *designed* to be legible in red light, and may not be usable with other colors. I have seen a planetarium globe which was inscribed in red and white which infuriated the maintainer because the markings disappeared under red "nightlights".

I have personally fooled with the CMG Infinity in Green, Blue-Green, Red, White, and Ultra White, all side-by-side with fresh batteries. The Blue-Green seems as bright as the Ultra, the Green only slightly dimmer, the White significantly dimmer, but the Red dimmer still. I'm sure this is a combination of the power effeciency of the LED's used *and* human eye sensitivity, but it is first-hand experience.

I use my BG Infinity all the time, and have noticed that my eyes can dark-adapt while the light is on. It's great to be able to walk into a dark room, light the CMG, wait a bit, then walk outside reasonably dark-adapted. However, using the light up-close can cause retnia blooms.

Also, this is hearsay, but scientificially reasonable and probably verifiable: the reason the military switched away from red was the IR emmissions. The red filters let alot of the IR from the lightbulb escape, and red LED's emit IR without (much) heat, because some of the output is on either side of the main wavelength. Actual IR light is much more intense than that emitted from warm objects, and is often used as secondary illumination for light-intensification goggles. Witness the Surefire M1, and the IR filters for their flashlights.

Anyway, I agree with the others: the only certain solution is the least amount of light possible, regardless of the color. The best solution may be a very-adjustable light, with many steps of intensity. No idea how to make it, but it would be nice to only have as much light as you need.


----------



## ikendu (Jan 9, 2003)

> Originally posted by Blikbok:
> *The best solution may be a very-adjustable light, with many steps of intensity. No idea how to make it, but it would be nice to only have as much light as you need.*


<font size="2" face="Verdana, Arial">Take a look at the Starlite or Skylite from the post above...smoothly adjustable!


----------



## cave dave (Jan 9, 2003)

I keep a yellow filter on my Opalec and use that at night to find the toilet and when camping. If I need more light I take the filter off.

Strange about the yellow filtered Opalec, It seems about twice as bright as an White arc but hurts my eyes much less. For that matter I've put the filter on a KL1 and it produces a Very bright yellow beam that still hurts your eyes less than say a Turq Arc AAA, while being much brighter.

The Turq arc makes me sqwint when I turn it on in the middle of the night.


----------



## snake (Jan 9, 2003)

ke ke




my adjustable light is done by my fingers.. 5 step adjustment: 1 fingers to 5 fingers

to preserve night vision.. I close one eye when reading map..so retain 50% of night vision

I don't like red as there are more red line on map then green


----------



## UnknownVT (Jan 10, 2003)

> Originally posted by Quickbeam:
> *Possible reason why our eyes like amber and turquoise monochromatic light better than others:
> <snip>
> 
> ...


<font size="2" face="Verdana, Arial">---
Many thanks for that "inspired" input











however, I don't see such good *definition* with blue-green/turquoise light as with yellow/amber.

Could well just be a personal preference/bias or my eye-sight.

However one might want to consider the following:

Blue light apparently is not focussed on the retina as sharply as the other wavelengths - hence the all the rage about "blue-blocking" sunglasses some years ago......"fad" or not, they do work, and are now quite commonplace - 
try some Serengeti Drivers (copper tint) - not only do color seem to be enhanced - reds literally jump at you - 

but more importantly distant vision and acutance is noticably increased - so much so that some have asked if those sunglasses were prescription - and I have also proven to others that one can see some distant objects much more clearly, when they went virtually UNnoticed with the unaided eye.

So to cut a long story short - 

blue light confuses definition - as someone else has also posted Annoying Blue LEDs - so the addition of blue as in blue-green - may well give more /better color rendition - 
the blue does not help one's definition - 

whereas yellow/amber is well known for definition enhancement - 

hence my bias for yellow/amber.


----------



## Quickbeam (Jan 10, 2003)

Excellent observation about wavelength focusing! Lots of good info in this thread.

Looks like you have to take into consideration all of the following:

For preserving "Night Vision":
Any color except red will break down rhodopsin at an intensity level where the color is identifiable as a color and not just "light".

Here, dim red wins out, allowing greater light intensity than any other color without breaking down rhodopsin and destroying night adaptation of the retina.

A dim red LED light may be the best light for this use.

For "Monochromatic light as general use":
Number of cones activated, greater numbers improve detail.
Focusability of the wavelength, improving sharpness at the right frequencies.

Amber and turquoise activate 2 of 3 cones.
Amber focuses better on the back of the retina.

Here amber/yellow should win out.

A bright amber LED light of any sort may be best here.

Sound good?

A special note about Scotopic vision (vision using rods) before someone else brings it up. Our Scotopic vision is best at detecting light in the turquoise range (even though Scotopic vision is black and white - using rods only), but once the light hits the intensity where you see "turquoise light", and not just "light", your rhodopsin is broken down and you lose your night adaptation for another 30 to 60 minutes as the rhodopsin builds up again... So a turquoise LED or LS shouldn't do you much good if you are trying to preserve your night vision since they're too bright, unless they are kept EXCEPTIONALLY dim.

These statements are combining all of the information above. Sound about right?


----------



## UnknownVT (Jan 10, 2003)

mucho admiration for good summary Quickbeam








Scotopic or "true" night vision was *rod* based - 

photopic or daytime vision is mainly *cone* based 

with the in-between-y *mesopic* vision using both cones and rods.... 

I think *mesopic vision* (as opposed to scotopic or "true" night vision) is probably what I am trying to preserve in a more urban type dark environment - as I am always "straining" to try to see more detail - 

- whereas pure *scotopic* vision would be viewing mainly from the peripheral vision - it would be blurry and only really good for distiguishing between lighter and darker and for detecting movement.


----------



## Quickbeam (Jan 10, 2003)

Whoops! I mistyped - I meant rods - I fixed the post - thanks!


----------



## Albany Tom (Jan 10, 2003)

Quickbeam - excellent summary!

I'd only add that, at least in my experience, even a single red LED light (Arc AAA) is enough to wreck scotopic vision. 

I'm very happy to learn all of this, and to know that what I was using in my old darkroom was my scotopic vision! The light was provided by a single 5.5" Kodak safelight with a 7 watt bulb and a wratten #13 filter. With the normal room lights on, you could not tell if the safelight was on! But if you looked directly at it when working, after your eyes adjusted, you would lose much of the dark adaptation. 

All this time I thought it was just my pupils getting bigger, and I never could understand why it took so long to adjust to the light! I think I want to buy one of those old safelights just to play with now....

Everyone, thanks for all this info!


----------



## Lux Luthor (Jan 11, 2003)

> Originally posted by UnknownVT:
> * </font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by Quickbeam:
> Possible reason why our eyes like amber and turquoise monochromatic light better than others:
> <snip>
> ...


*<font size="2" face="Verdana, Arial">---
Many thanks for that "inspired" input












however, I don't see such good definition with blue-green/turquoise light as with yellow/amber.

Could well just be a personal preference/bias or my eye-sight...

...blue light confuses definition - as someone else has also posted Annoying Blue LEDs - so the addition of blue as in blue-green - may well give more /better color rendition - 
the blue does not help one's definition - 

whereas yellow/amber is well known for definition enhancement - 

hence my bias for yellow/amber.*</font><hr /></blockquote><font size="2" face="Verdana, Arial">I've tested and compared all the colored Luxeons except the blue ones. I've done this over and over again, and not by shining them at the ceiling, or playing with them in the backyard, but by taking them out in the woods in the Adirondacks under very dark conditions. The amber (and red and red/orange) unquestionably allow one to see much more clearly than green, turquoise, or white. I've called this "clarity" or "depth perception" on other threads.

I have no doubt that it's not your imagination, or personal preference, or eye sight that makes you think you can see more clearly with amber. The focusing effect you mentioned makes a lot of sense to me as an explanation for this, but explanation or not the difference in clarity between, say, amber and cyan is blatantly obvious when using an LS. With single 5mm LED brightness levels, though, it may not be obvious at all.


----------



## carl (Jan 12, 2003)

That's it, I'm now looking for a YELLOW keychain light. I like our Inova microlight's constant-on switch because its bigger and longer than the thumbnail switch of the Photon. However, can't find a yellow Inova microlight. Who else besides Photon makes a yellow microlight with a large (not a tiny thumbnail) constant-on switch?


----------



## vcal (Jan 12, 2003)

> Originally posted by carl:
> *That's it, I'm now looking for a YELLOW keychain light. I like our Inova microlight's constant-on switch because its bigger and longer than the thumbnail switch of the Photon. However, can't find a yellow Inova microlight. Who else besides Photon makes a yellow microlight with a large (not a tiny thumbnail) constant-on switch?*


<font size="2" face="Verdana, Arial">Very much agreed! That's the very reason the Nighthawk amber "finger-light" was chosen by the Air Force for Desert Storm 10 years ago.
-Also, I believe the amber LED, besides giving much better acuity than most of the other colors, is also more efficient-only needing 2 volts+ to give decent brightness.

That Nighthawk light was the one that first got me really interested in LEDs (as illumination tools)-back in '95...before joining this educational forum. 

p.s.-those original Nighthawks are still available some places for as little as 12-$14., although Johnson-Smith Company still insists on charging $21.00+ for that versatile light (which seems to operat almost endlessly on just TWO worn out, inexpensive type #76/357 alkaline buttons.


----------



## UnknownVT (Jan 12, 2003)

OK now we're hearing from more people who favor yellow/amber as a mono-color light to see by.....

However one of the main concerns about gathering statistics is that the gatherer may have (inadvertantly) influenced the results








My own preference for yellow/amber - has been from personal experience and probably also from partly informed scattering of reading.

I knew *red* was traditionally used for preserving night vision (and I had also read about the claimed "myth" - that red was really a throwback to the use of a red safelight in photo darkrooms)

BUT for me I found it very difficult to see details/definition under the red.

I then read about *green* and *blue-green* - which to me seemed like the direct opposite to red - 
eventually also found out about the use of green or blue-green because of NV - (military) Night Vision equipment - and not necessarily to preserve the eyes' dark adaption.

HOWEVER despite the fact in the early days green and blue-green LEDs were said to be the brightest of all LEDs available - I also found that it was harder to see contrast and definition under those colors - espcially among woods or grass - where these green biassed colors do not offer much contrast.

I found from use that *yellow*/amber seems to work well for me for a mono-color light - the definition of details was good despite the fact there is (obviously) some problems with color rendition. In certain circumstances using yellow light seems to enhance contrast.

So for years I have had a yellow Photon 1 on my keyring as an EDC.

Some of my input on this thread is sort of *reverse reasoning* - 
ie: the yellow seems to work for me - now what's the reason?

I would love to read the explanation - and not just use my own arguments to convince myself - if you get what I mean...














Thanks for all the input 
and your patience


----------



## Albany Tom (Jan 12, 2003)

Well, I can throw out some more psuedo-data, and maybe that will make some sense to someone. 

We have a lousy ability to see red in our peripheral vision, but a great ability to see blue from the sides. This has been attributed to everything from people under the influence of drugs or alcohol having a tendency to "follow" their car right into flashing red lights, to people finding blue lights annoying. Yellow, as I believe Quickbeam pointed out, will light up both our red and green sensors, which may add to definition.

Personally, I find red AND yellow lights distracting, when used as an area light or flahslight, and prefer green, but for instrumentation lighting I like red or white, and find green distracting. I'm probably just weird, though.


----------



## Quickbeam (Jan 13, 2003)

Posted 2 new QA additions to my site using the data found here (and some picture examples). 

http://thelightsite.cruxial.com/qa.htm#colors

http://thelightsite.cruxial.com/qa.htm#nightvision

Enjoy!


----------



## Quickbeam (Jan 13, 2003)

"Some of my input on this thread is sort of reverse reasoning - ie: the yellow seems to work for me - now what's the reason?"

Actually, no reverse reasoning at all - read the blurb "choosing a color" that I wrote on my QA page as to why yellow is the better one for your eyes to see. The reasons are not statistical, but based on the biology of the eye and the perceptions of our brain.


----------



## UnknownVT (Jan 13, 2003)

> Originally posted by Quickbeam:
> *"Some of my input on this thread is sort of reverse reasoning - ie: the yellow seems to work for me - now what's the reason?"
> 
> Actually, no reverse reasoning at all - read the blurb "choosing a color" that I wrote on my QA page as to why yellow is the better one for your eyes to see. The reasons are not statistical, but based on the biology of the eye and the perceptions of our brain.*


<font size="2" face="Verdana, Arial">--
Thanks Quickbeam, I appreciate your re-assurance, and I certainly was not casting any aspersions - in fact I have already said that I stand in admiration of your summary.

However - getting back to *blue* light and the eye focussing problem that I brought up before in this thread - 

Thinking on this more - 
it is only the blue *wavelength* light that the eyes have difficulty focussing on the retina -
however any other wavelength that excites the blue receptor only, will not have the focus problem.

So why do some people have difficulty with turquoise/blue-green light - which is a mono-wavelength that uses the green and blue receptors in the eye as opposed to having a true blue wavelength content?

Is this more of a personal preference or individual eyesight - 
or is there a further *biological* (non-statistical) explanation why yellow/amber is apparently "better" than turquoise/blue-green? - 
even though turquoise/blue-green is also around the middle - just on the side of the eye's wavelength sensitivity spectrum (similar to yellow/amber)?

Thanks


----------



## Lux Luthor (Jan 13, 2003)

> Originally posted by carl:
> *That's it, I'm now looking for a YELLOW keychain light. I like our Inova microlight's constant-on switch because its bigger and longer than the thumbnail switch of the Photon. However, can't find a yellow Inova microlight. Who else besides Photon makes a yellow microlight with a large (not a tiny thumbnail) constant-on switch?*


<font size="2" face="Verdana, Arial">Unfortunately, I would have to say that I've never met a 5mm yellow LED that wasn't pretty dim.


----------



## vcal (Jan 13, 2003)

> Originally posted by Lux Luthor:
> * </font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by carl:
> That's it, I'm now looking for a YELLOW keychain light. *


*<font size="2" face="Verdana, Arial">Unfortunately, I would have to say that I've never met a 5mm yellow LED that wasn't pretty dim.*</font><hr /></blockquote><font size="2" face="Verdana, Arial">You guys need to try the 5mm Yellow from Hosfelt cat.#25-335 (75¢US)-8000mcd and *looks* like it it the dark.

That's the same Led that was used in the Nighthawk. _That same LED was $8. at a parts counter I went to back in 1992._


----------



## UnknownVT (Jan 14, 2003)

> Originally posted by vcal:
> *You guys need to try the 5mm Yellow from Hosfelt cat.#25-335 (75¢US)-8000mcd and looks like it it the dark.*


<font size="2" face="Verdana, Arial">--
Thanks for the reference....

In looking up this bright Yellow LED - 
I came across this very useful page:

The Brightest and Most Efficient LEDs and where to get them!
LEDs with Punch! by Don Klipstein


----------



## Lux Luthor (Jan 14, 2003)

> Originally posted by vcal:
> * </font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by Lux Luthor:
> </font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by carl:
> That's it, I'm now looking for a YELLOW keychain light. *


*<font size="2" face="Verdana, Arial">Unfortunately, I would have to say that I've never met a 5mm yellow LED that wasn't pretty dim.</font><hr /></blockquote><font size="2" face="Verdana, Arial">You guys need to try the 5mm Yellow from Hosfelt cat.#25-335 (75¢US)-8000mcd and looks like it it the dark.

That's the same Led that was used in the Nighthawk. That same LED was $8. at a parts counter I went to back in 1992.*</font><hr /></blockquote><font size="2" face="Verdana, Arial">Can you compare the output to the yellow Photon II LEDs? What about beam quality?


----------



## vcal (Jan 14, 2003)

That Toshiba (type-180) gives a very narrow 6° spot, and I measured its overall output as a "140", compared to only "85" on my yellow Photon-II. 
The measurement was done with the same batteries for both LEDs on my G.E.213 analog light meter.

That particular Led is also mentioned in the Klipstein link provided above (for the hottest Leds). There are 2 or 3 other excellent ones also listed there -for higher cost.


----------



## Ron Schroeder (Jan 15, 2003)

The most important factor for preserving night vision is the PERCEIVED brightness of the light. If it looks brighter, it will effect your night vision more. 

The second factor is the color related contrast of the subject. For example, if you are looking at blue printing on a white background, a red light will allow you to read the print at a much lower intensity then a blue or green light. If you are looking at red or orange printing on white, a low intensity blue or green light will be far better than red or amber.

So the general answer would be low intensity white light unless you have a specific color contrast situation that a colored light would enhance.


----------



## Quickbeam (Jan 15, 2003)

"The most important factor for preserving night vision is the PERCEIVED brightness of the light. If it looks brighter, it will effect your night vision more. "

True, but perception (interpretation of visual signals by the brain) occurs as a result of detection. The light will be percieved as brighter because the eye is better at detecting it. Rhodopsin, however, has a detection range which is limited.

I'm learning more and more about this (and remembering a lot of it from my Perceptions classes in college as well). Here's how it works: Rhodopsin builds up in the rods when it is not being bleached by light. In 30-60 minutes you have reached the maximum threshold of rhodopsin which can be stored by the rods (maximum "night vision"). As light intensity increases _in the range that is detected by rhodopsin_, rhodopsin bleaching increases.

The exception to this is red light around 620nm or greater (HELLO Red LED!). Your rods cannot see deep red light of this frequency or lower. If you only had rods in your eyes, red light would be invisible, the same way infra-red light is invisible to us because it is outside the frequency detection range of our red cones. 

Red frequency light (>=620nm) will be easily detected with the red cones but is essentially invisible to rhodopsin (the rods) - hence little or no rhodopsin bleaching and no loss of night vision, but you will be able to see with the red light. Turn off the red light and you still have your rhodopsin available for detecting dim light in the frequency range for rhodopsin (peak 500nm).

So, the dim red light will be perceived as brighter, but only because the red cones are now doing the detction and are more sensitive to the wavelengths. This will result in little or no loss of night vision via bleaching of the rhodopsin since it is essentially outside of the detection frequency of rhodopsin.

Orange, amber, blue, white and green light ARE in the detection frequency of rhodopsin and will cause rhodopsin bleaching in the rods, and therfore loss of "night vision".

Whew!


----------



## Lurker (Jan 15, 2003)

Question: 
Assume you illuminate something (a shirt, for example) with a red LED that is emitting a particular wavelength of light. Does the light that comes back to your eyes off of the surface of the shirt necessairly have to be exactly the same wavelength, or can it be changed somehow by the dyes in the fabric of the shirt? Does the intensity of the light have a bearing on this? I'm just wondering since it could have a bearing on the interesting things Doug just posted.


----------



## Quickbeam (Jan 15, 2003)

Unless the dye is fluroescent, it will only reflect back (or absorb) the wavelengths shined upon it.

Fluorescent compounds absorb light and re-emmit it at a different frequency.

Draw a picture with different color fluorescent markers on a piece of white paper. Sit in the dark and shine a blue LED at it and you'll see the picture in all the colors you drew with! Pretty cool!


----------



## Lurker (Jan 15, 2003)

This is related but kind of off topic, so I will apologize in advance. 

As I understand it, the human brain produces a hormone called melatonin at night to encourage sleep. Melatonin production is stopped during the day so you can be alert, and the way the brain can tell the difference between night and day is a simple response to the amount of light entering the eyes (darkness = night = sleepy). So if you wake up in the middle of the night and you want to go back to sleep, turning on bright lights can work against you by reducing melatonin levels and making you feel more awake. I wonder if these night-vision-preserving light colors would be less likely to inhibit melatonin production and make it easier to get back to sleep.

I know this is kind of off-the-wall, but there is a lot of knowledge in this forum. Maybe someone knows.


----------



## UnknownVT (Jan 15, 2003)

> Originally posted by Quickbeam:
> *I'm learning more and more about this (and remembering a lot of it from my Perceptions classes in college as well). Here's how it works: <snip>
> Whew!*


<font size="2" face="Verdana, Arial">--
WoW! Quickbeam - thank you so much for the great explanation.

Great to know that all those people have not been wrong all those years using *red* light to preserve true night vision (scotopic).

Whereas the use of green and blue-green was first to "preserve" the use of NV (Night Vision) *equipment* - and avoid detection by NV equipment.

But as some have discovered the use of *low intensity* lights help preserve the ability to see in the dark - hence the use of very low intensity green or blue-green since our eyes are most sensitive to those wavelengths and very little is needed - 
so the quest for the *"brightest"* green or blue-green is a mistaken belief that *color* is a panacea for preserving night vision.

However for some it is not necessarily the pure night scoptopic (rod) vision that we wish to preserve - but more probably what's known as *Mesopic* vision where both cones and rods are used - eg: at twilight - as a lot of people strain to see detail......

and as you explained previously for detail/definition - *yellow/amber* seems to be a good compromise without dazzling the user's dark adapted eyes.

Thanks.


----------



## Quickbeam (Jan 15, 2003)

Well, actually... (OH, cr*p... Here he goes again!) ...the yellow light will still mess up the buildup of rhodopsin and thereby disrupt rod-based night vision... Yellow light just happens to work out as the monochromatic color we can see the best with in general. 

You may as well just use a dim white light to preserve what is called "mesopic" vision - which is really nothing more than vision with a large quantity of unbleached photoreceptor pigment in the cones and rods - AKA "partially adapted to the dark"


----------



## UnknownVT (Jan 15, 2003)

> Originally posted by Quickbeam:
> *You may as well just use a dim white light to preserve what is called "mesopic" vision - which is really nothing more than vision with a large quantity of unbleached photoreceptor pigment in the cones and rods - AKA "partially adapted to the dark"*


<font size="2" face="Verdana, Arial">--
Yes, understood thanks - basically to "preserve" the mesopic vision *any* color will do -
it is the *intensity* that makes the difference for being able to see in the (semi-)dark when one switches off the light.

So there is only one color and that is *red* >620nm that actually preserves the pure "true" night - rod (scotopic) vision.

So something like the Rigel Systems Skylite - with selectable white and red LEDs and continuosly adjustable brightness levels - would seem a good light - as it would have red - to preserve the true scotopic night vision, 
but for when one actually wants to see details/definition (which scotopic is NOT good at) there is also a dim-able white.


----------



## Albany Tom (Jan 19, 2003)

This has been fun. I just did some tests, and confirm what Quickbeam and co. have come up with.

1. Sit in a dark room. Illumination was from outside moonlight, through a window, full moon, but overcast. It's dark enough inside that gen 3 night vision can see, but barely - noisy, blurry. To the eye, everything is a bit blurry, you can't see colors. This is scotopic vision, from what I've read.

2. Obervation - using the night vision monocular completely wrecks night vision for that eye, as expected. I've seen this effect before, it's weird as you have one eye that just isn't working right, but the other can see fine. (One of the reasons many suggest a monocular for night vision instead of a binocular headset, but that's another topic.)

3. Test - Try a red Arc AAA. As expected, this shows up bright red, and also hurts scotopic vision. Wait a few minutes for things to reappear...

4. Test - someone here had said they tried this walking at night - Use your hand as a reflector, blocking the direct light from your eyes, and illuminate the room with red Arc AAA light reflected from the palm of your hand. I held the Arc about 2 or 3 inches from my hand. This works! I could see everything clearly, but this did not seem to affect scotopic vision. 

A weird thing, though, is that the color did not appear to me to be red. It looked orangeish, or amber. My feeling is that I was seeing the light some with the red color sensors, and some with the monochrome sensors, and the color was blended. 

5. Repeat test 4 with green Arc AAA. This, as predicted, wrecks scotopic vision. The light appeared green, and much brighter than the red, even though with direct illumination the two colors appear to be about the same brightness.

This fits with the 620nm mark. The amount of <620nm light produced by a dim red LED is way less, I suspect, than any normally filtered incandescent lamp. Green output, for example, would be zero from the LED, but certainly something, even if 1,000 times less, from an incandescent through a filter. 

I've heard often that the red night filter was useless, as to turn it down low enough to not harm night vision it's too dim to be of much use. I've heard the SAME THING with respect to the old incandescent color safetlights. I know with LED's it's not true in the darkroom, and now I'm pretty certain that it's not true with night vision in general. A *dim* red LED could produce enough light to see and walk around with, in total darkness, yet not affect your scotopic night vision, which takes minutes to aquire, at all.


----------



## Moth (Jan 19, 2003)

What is the brightest amber/yellow LED flashlight commercially available?


----------



## UnknownVT (Jan 20, 2003)

> Originally posted by Albany Tom:
> *This has been fun. I just did some tests, and confirm what Quickbeam and co. have come up with.
> <snip>
> I've heard often that the red night filter was useless, as to turn it down low enough to not harm night vision it's too dim to be of much use. I've heard the SAME THING with respect to the old incandescent color safetlights. I know with LED's it's not true in the darkroom, and now I'm pretty certain that it's not true with night vision in general. A *dim* red LED could produce enough light to see and walk around with, in total darkness, yet not affect your scotopic night vision, which takes minutes to aquire, at all.*


<font size="2" face="Verdana, Arial">--
Nice experiment.

Red is definitely a difficult color for me to make out details/definition by - and like you've suggested with red I seem to need much higher brightness - which seems to defeat the purpose of preserving night vision.

A lot of us live in urban environments and the amount of "light pollution" is extremely high.

For example for me - any room with windows will be affected by external lighting (eg: street lighting) - to exercise scotopic (rods only) vision, I have to use a room without windows and stop up the gap at the bottom of the door to prevent light leakage.

If a lot of people have to go to this amount of trouble to be able to get "darkness" - I think, in my case it isn't true scotopic (rods only) vision I am trying to preserve but some level of dark adaption for my eyes (mesopic vision?).

I know for example if it were dark enough for me to be using true scotopic vision it would be uncomfortable (as I would not see colors or make out any details) then I would more than likely 
use that d*mned light I EDC in my pocket!!!












What color light?

Well red would not be so good (for me) as I am more than likely wanting to details/definition - and red would need much higher brightness for me - so red would be as bad as some other color at lower brightness levels.

White? I definitely see "better" with that - but it seems to shock my eyes more - so I use that if I don't care about saving my dark adaption - ie: I've decided to use a flashlight.

But if I want to use a light only sparingly/intermittently - then I prefer to use a dim yellow - like the Photon 1 yellow I EDC - despite the fact it is old and doesn't even have a constant on/off switch. 

I think it works for me because (1) I actually see definition better with yellow (YMMV) (2) yellow seems to glare less than other colors for me, (3) the fact I am using the light only intermittently means that most of the time I can get away without a constant on switch.....


----------



## Albany Tom (Jan 20, 2003)

For bright amber, I think this would be the place to look:

http://www.inretech.com/

Scotopic vision is, to me, fun. It takes a while to get down to that level, but once you do, you'd be surprised how well your eyes work. Very close to the ability of good Gen 3 equipment. 

I know what you mean about light pollution. If you're not seeing scotopic, then I don't think it matters much what color you pick, so I'd suggest something that you're comfortable with. The Arc-AAA's are to me bright enough that they'll cause your pupils to constrict some, which I suspect is the logic on dim lights affecting mesopic? vision. This effect is annoying, and I believe what people are usually talking about when talking about "night vision", but it takes seconds, not minutes, for your pupils to dilate again. Seems like a dim yellow Arc AAA would be perfect for this, but I don't know if they were ever made, and knowing Arc they'd be too bright.

I finally built a dim red light! I used a Brinkman 1 AAA light, an 8000mcd red LED, an A23 battery, and a 6.8k ohm resistor. (Yes, 6.8k ohm) Current is 1.55mA. It's about 20 times dimmer than a red Arc, and it works great! Before your eyes adjust to scotopic vision, it's bright enough - barely - to see to slowly walk around. After your eyes are in scotopic vision, the light shining on white objects more than arms length away won't degrade your scotopic vision. 

It's a weird effect, you can see the red color, and things are clear, but as soon as you turn the light off you still have your fuzzy scotopic vision. It's truly a flashlight that won't wreck your night vision, but in scotopic mode it's quite useful. This may become one of my favorite lights.


----------



## UnknownVT (Jan 20, 2003)

I'm trying to rationalize my flashlight choices (almost after the fact).

I existed on a Photon 1 yellow EDC for years because it gave me a shot of light when needed, that I could still see good definition by - but was dim enough so that it did not hurt my eyes' ability to see in the dark (probably as we suspect really only mesopic vision as opposed to the real scoptopic (rods) vision which is fuzzy and colorless).

The dim yellow Photon 1 - seemed adequate for most close personal tasks - and even for the occassional walking in the dark - both outdoors and indoors. I think the yellow helps in contrast and definition to make out holes and obstacles. 

I considered it OK for walking outdoors in an emergency - afterall that's one of the things an EDC is supposed to fulfill - but I did not consider it "ideal".

For outdoors walking I preferred a brighter light that was white - just for better color rendition - I looked for one with a single common cell like AAA or AA that was bright enough - for me the *minimum* was to illuminate at least 3 feet of ground in front of me, with the flashlight held in the hand naturally (ie: from about 3 feet off the ground). But I also realized this kind of flashlight would "sacrifice" my dark vision.

The softer more even wider hot spot of a white LED seemed kinder than any incandescent light other than perhaps the very dim Maglite Solitaire - despite being distinctly yellow did not for me seem to offer good definition - probably because of the very narrow hot spot when focussed - but any wider angle gave very uneven beam.

I liked the CMG Ultra (I bought the Ultra-G ) because of its use of a single AA cell - and the larger size (over the ArcAAA) was fine as it would EDC in my other pocket for the specific use for outdoors walking and when I need a brighter light and better color rendition over the dim yellow Photon 1 - 
but on the understanding this light will disturb my dark vision much more - 
however the dark adaption for mesopic vision is only in matter of seconds, as long as the eyes aren't "shocked" by very bright light - like looking directly at lithium powered Xenon bulb lights......


----------



## ali5mith (Jan 24, 2003)

I believe this debate as to which colour of artificial light has the least effect on vision adapted to viewing objects in natural night light (moonlight) started with the military close to the beginning of the last century. It was considered by them that since moonlight contains no red light, using a dim red light to look at a map or other printed or written items while under a cover to stop leakage of the light, would have the least effect on night vision when back in the open air and viewing the surroundings illuminated only by the blue and green of moonlight.
It is true that when looking at glowing light green gives better definition than than red, but also please consider that as far as the military is concerned any steady red light seen at night can only be man-made and a giveaway of position to an observer.


----------



## Canuke (Jan 24, 2003)

Quickbeam and UnknownVT:

While their may be advantages of turquoise and yellow because they trigger two sets of cones, I can be sure that this does not affect resolution.

The reason why monochromatic lights seem to sharpen things up, is because chromatic aberration is minimized. Different wavelengths have slightly different focal lengths, and human vision must average them out. I believe that the eye, by design, weighs the average in favor of red and green when determining focus, because photopic vision is most sensitive to them. As a result, blue is mis-focussed a bit; that's why blue and violet LED's have that "blooming" effect.

If you have normal vision and a point light source, you will find that if you "focus too close" the blurred light has a blue fringe; when you focus too far, the objects have a red fringe.

The eye is also designed such that close focus requires a muscular effort, but far focuss is only a relaxing action. As the lens hardens up with age, it doesn't focus as far out anymore, so the blue fringes show up more than the red ones.

Those who tend to hold things away from their faces to get it in focus, would actually benefit a bit from blue light.

That's why magenta lighting, which contains red and blue, are the fuzziest lighting of all because the red and blue images don't line up and strain the eye as it "hunts" back and forth, usually settling on red.

Blue blockers sharpen everything up by eliminating the least-focussed color bands from vision.

That's probably why I find twilight to be the worst time for blurry vision while driving -- the headlights aren't helping yet, but there's a lot of ambient blue and the irises are wide open.


----------



## UnknownVT (Jan 27, 2003)

Very good observations Canuke - especially about the magenta lighting.

However isn't magenta also a mono-wavelength light - in that it is only exciting the blue and red receptors on our eyes and it isn#t that the light is a compound wavelength. So if it is our eyes' lens that has the chromatic aberration/focussing difficulty then it really shouldn't be affected by a single wavelength magenta light, right?

Shouldn't the focus shifting difficulty apply only if the magenta light is made up of separate red and blue wavelengths?

I do a lot of music/stage photography and sometimes I do notice a difficulty focussing my eyes and I do think it is when there is a predominance of magenta - but I am not sure if it is made up of using a combination of separarte red and blue filtered lights, or whether it is using a magenta filtered light.

Good observations though - I look forward to further discussion on this focus shifting effect.

Thanks


----------



## Quickbeam (Jan 27, 2003)

I believe that Magenta is the only color (besides white) which cannot be monochromatically produced. This is because they are at opposite ends of the visual spectrum and the spectrum does not "wrap around" to put red next to blue. If it did, this would allow an average between the two (magenta). Instead when you try to average red and blue, you get yellow, since it is between the 2 on the spectrum.

This is based on what I read about this topic on one of the CIE color chart sites. Corrections appreciated if incorrect.


----------



## Canuke (Jan 27, 2003)

The relationship between magenta and violate is the one discontinuity between the RGB perception model and the real-world fact of wavelength. For this discussion, I use "magenta" to designate red+blue light, and violet to mean the actual monochrome wavelength (400-420nm). Quickbeam is right in that there is no such thing as a single "magenta" wavelength; the wraparound occurs in the human brain's modelling of visual data, not in the physical wavelength.

I've been trying to come up with a test to determine whether violet light actually does excite the red cones, but I'm unable to figure one out. I suspect it isn't possible, short of finding someone whose retina only has red cones. It sure seems like it does; the RGB model's depiction of violet as red+blue doesn't seem to look wrong.

While both violet and magenta are fuzzified due to chromatic aberration, the particulars aren't the same. Magenta gets fuzzy because of the disparity between its red and blue components, while violet is fuzzy because of the focus-weighting I mentioned. It is possible for the eye to compensate for the latter, because it is monochrome (either by willful refocussing of the eyes, or using glasses), but not the former -- the eye is forced to choose between red or blue. NOte: it doesn't matter whether magenta is derived from adding red and blue lights, or magenta filtration -- magenta filters merely subtract green, UNLESS it's Woods glass.

Modern camera lenses don't show this effect, because they are engineered to eliminate it -- but you can see the same effect with a simple magnifying glass. Remember when you were burning things with one? When the lens was too close to the target, the blurred image of the sun had a reddish fringe... when it was too far away, it was bluish. 

Experiment: Assemble a group of different colored LED's in a row, all the same distance from the lens, and focus them on a white card with a simple magnifier (long focal length makes the effect easier to spot). Now do that with a magenta light (like one of those Sauce units).

Photographers may recall that SLR lenses have a different mark for infra-red focus... that is due to this effect. The longer the wavelength, the longer the effective focal length is.


----------



## Albany Tom (Jan 27, 2003)

ok - another test....

I have an advantage over most folks for this test. Without glasses, I'm pretty nearly blind, very nearsighted. I found a white card with black writing, and my two handy colored Arc AAA's, one red, one green. I wish I had blue, but this is what I have to work with. So I went into a dark room, and here's what we have:

First test. Hold the lights at distances so they are both visually the same brightness. This makes the white paper kinda orange/yellow colored. Now observe the lettering under green and red. First thought - sharper with green! Then I went back and forth. Here's what I think I'm observing, with my truly minor amount of photographic knowledge thrown in. Both lights are equally sharp. However, the green light seems to have higher contrast, even though it's equally bright. I'm wondering if this is what Quickbeam could be seeing with sharper amber than red, and the visual effect of two types of cones firing.

Test two - which one can focus closer? Answer - for all practical purposes, the same. By this I mean I can't tell the difference at all. They both have to be very close. This is tough to draw anything from, but on the other hand, I walk around all day long with pop bottle thickness single lenses. If chromatic aberration was a serious deal, I'd be bugging me all day long, far more than most people. The only time I notice this is in the periphery, when looking sideways at things with deep blue/near UV content - mercury vapor lamps for example. I don't notice any improvement in sharpness from monochrome vs broad spectrum lighting.

Let me throw this out: In photography, those in search of a sharp print used to go to "point source" enlarger bulbs. They'd use low voltage halogen lamps instead of frosted ones, to gain an increase in contrast. For a fact, "hard" or non-diffuse lighting casts more distinct shadows and creates higher contrast than diffuse lighting. (I kinda like that effect.) Anyway, what I'm getting at is that a green or red LED is pretty much a point source. The light comes from a very small area, and is projected. A white LED has a glowing phosphor, and the surface area is a lot bigger. Everyone has noticed this effect - white is more even. 

So I'm thinking all of this could be why the ambers seem to be sharpest. First, highest contrast because of color, lights up both the red and green cones; next no chromatic aberration; finally, it's a point source. A test would be to find something that lights up the green and blue cones, and test against amber. Hey, that would be cyan/turquious! Another favorite "bright" color. Coincidence?


----------



## balticvid (Nov 10, 2003)

....


----------



## balticvid (Nov 10, 2003)

Sailors have been using the red color foe a century.
How did they know to do that back then?

BMW dash board lights have been red ever since I can remember.


----------



## Quickbeam (Nov 10, 2003)

Trial and error? /ubbthreads/images/graemlins/smile.gif


----------



## VidPro (Apr 5, 2005)

i will comment , even though i shouldnt. things that SEEM to me, to be a certian way, and how that might be utalized, depending on what your DOING.

SPYING & HIDING
a color that is seen easily at night, is also seen easily by OTHERS 
a color that blends into your present atmosphere that you in, might give you the best light while you can still see what you want.
a light that cant be seen as well by what your stalking also becomes important (as already discussed)

EX: if your sneaking around in the woods with moonlight hitting green things, mabey using a light color similar to your surroundings would blend in the best. the dim moonlight blue green 

now REVERSE all that 
the thermostatic controlls:
other than what is easily triggered in your eyes when very dark, like the colors that your most sensitve to when your eyes have adjusted (as discussed)
there is also the balancing act, that seems to be done by your eyes and brain.
*look at blue long enough, and your eyes and brain have triggered in that color for so long, they are more sensitive to OTHER colors (not blue).* 

this can be observed by looking at ANY color for a long time, or even being Under a specific color of light, then looking at a white piece of paper under a full spectrum lignt.
what you see MOST is the color you WEREN'T looking at.

ok so you understand what i am getting at?
if you wanted to see the green trees (light off), you would prefer to have been looking under red NOT green.
if you wanted to LIGHT up the green trees (light on) you would be better to use green.

but if your reading a book in Red, your thermostatic controls are going to reduce your sensitivity to red, which wont reduce your sensitivity to green in dull lighting.

that is just how it seems it works.
if you use a COLOR , you will reduce your sensitivity IN THAT COLOR over time, when you look up or away, anything that is NOT that color will show up better.

by using a color, your keeping your sensitivity in other colors when you need it (preserving night vision)

colors that are mixed up like red-orange blue-green are going to change your sensitivity to seeing other things in the 2 colors not one, even though it might be balanced between the two depending on the spectrum (meaning eyes arent RGB or 3 bit).

by analizing your decreased sensitivity under the color your using, and how it can apply to keeping your sensitivity for what you want to see when your not using artificial Illumination.

mabey a amber would work great as your artificial illumination, if when you stop the amber, the light you now have to see by is the blueish moonlight.

and to have a reverse example for the red.
if you wanted to see how much blood is comming out of something with no illumination, then you would have been better off reading you book with a green light 

i hope i said that right, the idea i presented, might be to analize what you WILL need to be sensitive TO , when you are no longer artificially illuminated. or what light you will have for ambient when you shut off your source.

its the eye brain balancing act that occurs to thermostatically (meaning balance like a thermostat) increse your sensitivity as needed in any situation the human could be placed in.

so Everyone is basically correct about the COLOR they think is right. any ONE color will keep you able to be sensitive to other things. analize what you want to accomplish through it.

if its Lighting stuff up using the least ammount of energy, then the cyan, or that high sensitivity thing is great.
but the thread was *preserving* the rest of your sensitivity.

if the "british are comming", then use a green light  to see them best in the dark when you shut off your light.
or use a red one so they dont see you because of the colors they are around.
and if they are green army guys, then . . . you better use whatever dont get seen by them night vision stuff (as discussed)


----------

