If I understand correctly, the wavelength of the red light helps to keep your eyes adjusted for low light. I've never seen any actuall night vision equipment that had a red display, but then again I havn't seen much night vision EQ at all.
Red is just dimmer than most white lights. When you add a red filter, you reduce the total amount of light coming out. It also makes it harder for others to see your light for the tsame reason. There are arguments that other colors work just as good, or even better, but red was the color selected by the US Miltary, and so everyone goes with that.
As a 24 year veteran of the USMC, we were always taught that red was used for seeing at night for the following reasons:
Since red is a "dimmer" light, your pupils don't constrict nearly as much when you are viewing things in red light. Hence, when the red light is turned off, your pupils are still opened wider requiring less time for your eyes to readjust to total darkness. Also, it's harder for those that you don't want to detect your light to see red light.
The "display" color (green) of Light Amplification devices or night vision goggles has nothing to do with retention of night vision. Devices such as this have green displays because since the eyes are so sensitive to the color green it's far easier to pick out details on a green display than it is any other color. This is important because the displays on most night vision devices are extremely "grainy", and the green color helps to keep details that would be lost with other color displays. The down side to a green display is that since your eyes ARE so sensitive to the color green, when the night vision devices are taken off it takes considerably longer for your eyes to readjust to total darkness than with red light. Green light makes your pupils constrict further since your eyes are so sensitive to this color.
For viewing things in the dark with minimal effect on your night vision, red is by far the best color. When wearing night vision devices, retention of regular night vision is of minimal importance because that's what the night vision goggles are for in the first place! But to just plain see in the dark without losing your night vision red is STILL the color.
...simple exercise: view something in the dark with a red light, turn the light off and see how long it takes for your eyes to readjust to total darkness. Now, view something in the dark with night vision goggles, take them off and see how long it takes your eyes to readjust to total darkness. With the NVG's it will take your eyes more than twice as long to readjust to total darkness than it did with the red light...I know; I've done it MANY times.
and there is still a lot of controversy over which color is best for preserving night vision........
<font color="red">Red</font> is the correct color not to disturb true night (Scotopic/rods only) vision - as the rods in the eyes are INsensitive to wavelengths >620nm - which is <font color="red">Red</font>, so that color will not affect the rods.
<font color="green">Green</font> and Blue-Green - are used to "preserve" compatibilty with NV equipment - not the eyes.
Both these wavelengths are the ones the eyes are MOST sensitive to -
<font color="green">Green</font> for Photopic or daylight cone vision and
Blue-green/turquoise/cyan for Scotopic/rods vision.
So if you follow this logic any relatively bright source of light in green or blue-green is going to affect the eyes' dark adaption/night vision the most.
A lot of controversy arises simply because there is a lot of confusion between
(1) being able to see by a particular (dim) colored light well
(probably personal choice - but yellow/amber does well, white gives better color rendition.)
(2) using a color light so one's night scotopic vision remains unaffected
(red is the correct one here)
(3) using a color light compatible with NV equipment
(definitely green or blue-green)
(4) using a color light to see by that affects one's dark adaption (not necessarily true scotopic vision) least - ie: gives good recovery
(almost any color - it's probably more of a function of how DIM the light is - but there are preferences for yellow/amber as one can see well with this color at low levels and the color does not dazzle - evidenced by the long time use of amber fog lights that are said not to dazzle when reflected by white fog)
(5) what color light is the best to be seen - ie: noticable
(again probably personal choice - but anything that gives higher color-contrast to the ambient environment will tend to get noticed - and there is something to be said for Blue - hence the choice of blue for police lights)
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It's somewhat of a myth. Certain wavelengths of green light are superior for night vision.
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Actually the presumed ability of green light to protect your "night vision" is a modern myth. Since the light detecting pigment in the Rods are so sensitive to green light, green readily destroys your natural adaptation to darkness.
I'll try to keep it short.
Your Rods in your retina are most sensitive to dim light. They use a light sensitive chemical called rhodopsin to detect the light.
The rhodopsin "bleaches" or breaks down when struck with light - it's this breakdown that is detected by the nerves and that makes you "see" the light. The more rhodopsin that builds up in the rods, the better you can see really dim lights. It takes up to an hour to build up a full compliment of rhodopsin. Even starlight causes the bleaching (when you look at the stars, you detect it, hence the breakdown is occuring), but the rhodopsin builds back up easily since there was so little breakdown from such a dim light source.
A bright light in the detection frequency of rhodopsin instantly breaks down the rhodopsin that has built up - it's really sensitive stuff. Rhodopsin's detection frequency goes down to about 610nm. Dark red (and red LEDs) is below this frequency, so your Rods can't "see" red light. They are blind to it. You can blast your eyes with a really bright red light and still have your night vision for gazing at the stars with the Rods when the red light is turned off.
Green, however, is definitely in the detection frequency of the Rhodopsin and will bleach it right out. Green light = at least partial if not total loss of your natural "night vision" or "night adaptation" depending on the intensity. You then get to wait for up to an hour for the rhodopsin to build up again.
This is all proven via scientific experiments you can research at the library or your local college.
People think green is good for night vision due to their experiences with night vision equipment. This has resulted in the modern myth that green light preserves your natural night vision. This is not true and has resulted in a great deal of non-research based marketing by people trying to sell green LED lights.
I really think that people have known for a very long time that red light preserves night vision and want a "new and modern" way to preserve night vision, thinking that red light is the "old fashioned" way. However, our eyes havn't magically evolved over the last 50-100 years to suddenly accept green as a night vision preserving color. Let the buyer beware. Dark red light is your only choice for preserving 100% of your natural rod-based night vision due to the anatomy of the eye and can be used at intensity levels that allow normal navigation and operation without night vision loss.
You CAN use a really super dim light of any color - about the brightness of starlight, which will break down rhodopsin slowly enough that it can make up for the breakdown on the fly. However all the LED products I've seen are way, Way, WAY too bright for this. Plus the whole idea of using red light is so that it can be bright enough for you to operate pretty much normally without losing your night adaptation. Using a super dim light won't allow anything close to "normal" operation.
Just for fun, let's see if we can put this whole "green preserves your night vision" fallacy to bed once and for all.
If you think you have evidence to prove any light color besides red preserves naked eye night vision at intensity levels above that of starlight, prove it. Research abounds showing over and over that red preserves naked eye night vision and although I don't have the papers in front of me, one weekend at the local university will uncover more than enough research. I know because I studied this topic back when I was in college in my "Sensations and Perceptions" class and had to learn the biology behind it.
Site the research paper that shows green, or any color besides red, preserves naked eye night vision at intensity levels above that of common starlight. Let's see the research. We're talking real research here, not web pseuto-intellectual, pyramids-are-power-generators, backyard "I think it's brighter", wannabe research posted by joe shmoe. Real "double-blind-studies, dissections-and-chemical-analysis, find-it-in-medical-journals-and-textbooks" research.
Make it a game - a scavenger hunt of sorts. Have fun and let's see what you find (or don't find!)
Whether I'm right or wrong, we all learn something! [img]/ubbthreads/images/graemlins/smile.gif[/img]
The following is an excerpt I wrote some time ago on SIDB on the subject on how to improve and speedup dark adaption. It might also help on this subject:
>Originally posted by ProSec104:
>1)Wear red-lensed sunglasses just prior to nightfall. (...)
>Originally posted by Unicorn:
>It doesn't have to be red tinted sunglasses. Any color >will work.(...)
I don't want to bring an old topic up again - and I have to say that I don't have any tactical low light experience at all - but from looking at it from the physiological side only red tinted glasses will work as hoped/expected. Seing as good as possible in darkness has to do something with the rods (cones are for color seing which you don't use when night-vision adapted!) inside your eyes (and here part of that Vit.A story is important!) and them being very sensitive to special wavelengths. If exposed to lightwaves of certain lenght, a substance (11-cis-retinal to be exact) is converted from one to another state(don't worry, this is part of the seing process, so it's normal ). And this substance is very sensitive on light in the range of 500nm therefor you have to wear red tinted sunglasses (which only let light through in the 600nm range to the retina) to keep these substances in the rods from "falling apart"/converting (the higher the concentration of unconverted substance in your retina the more sensitive you are towards smaller light sources) and therefor being more sensitive when it gets dark and therefor faster night vision adaption. Nightvision adaption takes takes that long because this substance very easily transforms from unconverted to converted but to reverse the process it takes longer, it sounds strange and unbelieveable but your eyes are fully night adapted after about 30 - 45 minutes, saying at that point of time your ability to see in the dark is the best (since the concentration of that substance is at its max.
BTW: eating carrots is healthy but - as far as I know - you don't have to worry about having a lack of Vit. A because this stuff is nowadays in nearly everything we eat (artificially added).
My conclusion out of this is that the only light that can improve your night vision and help while navigation through the dark is red light. All other colors will have a negative influence on the nightvison adapted eye.
All I can say is what my own eyes perceive...I'll do some "perception tests" tonight with my own eyes again. It just seems to take less green (pretty sure we admit that we've read data the indicates our eyes are indeed more sensitive to green, however it's recovery time we are questioning, yes?) and I can see so much more contrast & area with green.
Though I have several green, turquoise, cyan, & red torches, the ones I've used for this personal perception test in the past are EternaLight Ergo 3s - one with the red/white & one with the green/white options (with only the color LEDs on of course). I like the EternaLights for this test because of the variable dimming ability of the light. I can step down from full brightness to max dim...
One thing I will "consciously" try to check will be the perceived "recovery time" of my own eyes. But with all the scientific data available, I think it will still boil down to results isolated to an individual's eyes & brain...That's probably where all the confusing conversation comes from, eh?
Quickbeam is dead on about this, but there's a point that may be missed.
When talking about scotopic vision, when you're using your rods to see with, you are NOT seeing colors. You're seeing somewhat blurry monochromatic images. It takes several minutes of near total darkness to achieve this. (starlight is too much light, as is the glow from a decent sized city.)
I also could be wrong on this one, but my experience seems to indicate that even a typical single red LED light is enought to wreck scotopic vision. I don't know if this is because there are components of the light shorter than 620nm, or if there is some degree of sensitivity below that, or if it's just my imagination.
In any event, a really dim red LED can be used as a light, then switched off, and you retain perfect night vision. You *can't* do this with a green led.
Enhancing and Maintaining Dark Adaptation: For maximum utilization of scotopic vision, 20 to 30 minutes are required, in total darkness, to attain satisfactory dark-adaptation. A more practical alternative is to have the aircrew members wear red goggles to facilitate dark adaptation. Red goggles can be worn in normal illumination and do not interfere significantly with the ability to read maps, charts, manuals, etc. They block all light except red light, and red light does not simulate the rods, as we have seen.
To understand why red filters can be used to achieve dark adaptation, it is necessary to examine the relative positions of the photopic and scotopic sensitivity curves in Figure 8-20. If a red filter with a cutoff at about 650 nanometers is worn, essentially no light is transmitted to the eye that can stimulate the rods. However, the cones are sensitive to the red light, and, thus, adequate visual acuity is permitted. By wearing red goggles for 30 minutes, the rods are almost fully dark adapted. Although the cones are not dark adapted, it only takes about 5 to 7 minutes, after a pilot steps into the dark, for the cones to adapt. Cone adaptation is relatively unimportant, since they are incapable of functioning in starlight illumination. There are, however, some drawbacks to wearing red goggles. For example, when reading maps, all markings in red ink on a white background may be invisible. In addition, red light creates or worsens near point blur in the pre-presbyopic or presbyopic pilot, as red light comes to a focus behind the retina and requires more accommodation to bring it into focus.
Dark adaptation of the rods develops rather slowly over a period of 20 to 30 minutes, but it can be lost in a second or two upon exposure to bright lights. The night flyer must, therefore, be taught to avoid bright lights. Also, the instrument panel must be kept illuminated at the lowest level consistent with safe operation, and the flyer must avoid looking at flares, after-burner flames, or gun flashes. If light must be used, it should be as dim as possible and used for the shortest possible period.
Dark adaptation is an independent process in each eye. Even though a bright light may shine in one eye, the other will retain its dark adaptation, if it is protected from the light. This is a useful bit of information, because a flyer can preserve dark adaptation in one eye by simply closing it.
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.
I hope this clarifies and confirms what Quickbeam and I have been trying to say.
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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.
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This is where the misconception of green or blue green light preserving human night vision comes from. The big problem here is that manufacturers have latched onto this statement without using their brains and are producing very bright green LED products that they claim will preserve night vision. This claim is patently untrue.
BTW, I read the Dr. Walt post and he forgot to mention that although the rods are most sensitive to blue-green (this is very true), blue-green light at an intensity level bright enough to discern the color and not just "light" will bleach out the rhodopsin rapidly and as a result, compromise your night adaptation. That's just the way it works.
Red is the only color to preserve night vision at intensity levels where you can work somewhat normally. Very dim light of any color will be usable without significantly compromising your natural adapted night vision, but if you can "see the color" of the light, it's degrading your night vision. The exception is red, which the Rods are essentially blind to. The important point here is that you can't operate equipment, write in a notebook, etc, by just starlight, at least not with accuracy. You need a more intense light to see with that won't compromise your night vision when it's shut off - hence the use of red light.
The frequency of the red light is also important. The deeper red, the less of it the rods can see. Orange or "high reds" (some LEDS are higher frequency than others) will diminish your night adaptation by bleaching the rhodopsin in the rods.
In reference to Albany Tom's point: The effect where you turn on a BRIGHT red light and it seems to kill your vision is actually the red cones getting shocked because you are going from a completely dark environement to a bright red environment. As a result you'll see afterimages from the bright red light bleaching the pigments in your red cones, sort of like what happens when to look at a sun lit scene after being in an office all day and then go back into the office. You can't see well at all.
The red cone visual field overlaps the rods, and makes it harder for your brain to distinguish the difference between the two when the red cone field is full of afterimages. Hence why a dim red light is recommended - not because bright red light compromises your rod-based night vision, but becuause it affects the red cones so profoundly that you perceive the afterimages as overlaping your rod's field of view. Bright green light would do the same, but would also bleach the pigments in the rods, destroying your night adaptation completely.
Still waiting for research proving that green light preserves night vision (at levels above that of starlight AKA where you see the color, not just "light" - all green LED products that claim to preserve night vision are bright enough to severely degrade night vision)! [img]/ubbthreads/images/graemlins/smile.gif[/img]
Thanks VT - that's a very helpful reference and hopefully clarifies things for a lot of folks.
Dano's reference web site about night vision states that:
"Once again; we should use the absolute minimum amount of light. This discussion is only about very low levels of light, any benefit of using green light to read charts will not be realized when the illumination level is excessive."
Again, the green LED lights being produced that claim to preserve night vision are WAY too bright to actually do so. The only exception to this is the astronomy-dimable-starchart type lights that can be dimmed to extremely low levels. However you could use a more intense red LED light without compromising your night vision and since it is more intense and you have more light to see with, you can operate more effectively. The entire website is talking about exceptionally low levels of green light and discounts the fact that the rods are insensitive to red light, which the red cones can then percieve separately and can therefore be relatively much more intense.
Conclusion (and hopefully an answer to the original post):
Extremely dim light of any color will preserve night vision, since that what night vision is for - for seeing in extremely dim light. At these EXTREMELY dim levels, blue-green is the light wavelength we are most sensitive to, and therefore can be used at lower intensity levels than any other extremely dim color. Red light preserves night vision at a higher intensity level than any other color since the dim light elements of the eye are insensitive to red light. This allows you to operate more effectively in your environment with red light as a result of the greater light intensity possible and therefore more detailed perception of the environment by the red-sensitive elements of the eye without disrupting your night adaptation.
My fingers hurt... [img]/ubbthreads/images/graemlins/wink.gif[/img]
Quickbeam - that "shock" effect fits exactly with what I've experienced with bright red LEDs.
The red LED light I made for keeping the night vision runs about 2 or 3 mA.
I can't be certain, but I'd be willing to bet, that red LED's allow a much brighter red light to be used in preserving scotopic vision than the traditional filtered white light approach. I'm betting this on the guess that a red LED has a sharper cutoff of light below 620 or 650nm than a typical filter. The deep red filters we used in color darkroom work were *much* dimmer than red LED's used for the same purpose, to the point that most darkroom people that have never used LED safelights refuse to believe they work until they've tried them.
Philips has one of those energy-saving lamps called a softtone in the form of a normal lamp, but with a pinkish coating which generates a kind of soft red light. I have one of these in my room and I have noticed that you can switch it on and off almost without loss of night vision, which isn't the case with the other colors. I know it uses about ten watts and that's more than enough to light the entire room for reading.
I know the "Softtone" lamps, and to be honest, the amount of light produced by them is sufficient to kill true nightvision.. Did you ever try to go into a really dark enviromment afterwards? [img]/ubbthreads/images/graemlins/icon3.gif[/img]
You definately loose a lot of your nightsight, due to the shear amount of light produced by the Softtones...
I didn't mean to say that it does give you perfect night vision, I just wanted to say that the pink softtone lamp seems to give off much more light than the white ones do once you get used it. I found that I could see a lot more in my room with the pink ones than with the other colors available.
Yes, this could be normal...incandescent lights give most of their visible light energy in the red part of the spectrum. If you take, lets say, a blue color filter, the amount of light that passes the filter is much less, so this could be a logical explanation.
Wim, as I understood they are not incandescent but cfl, wich means there isn't much ir radiation produced... [img]/ubbthreads/images/graemlins/rolleyes.gif[/img] [img]/ubbthreads/images/graemlins/icon3.gif[/img]
They are cfl, but I think the difference is simply the color of the light. Red light seems to be kinder than white light to night vision. I can't take pictures to show it (unless someone invents a camera with working eyeballs [img]/ubbthreads/images/graemlins/smile.gif[/img] ) But then again, it might simply be that there is less light with the pink/red lamp.