Yellow-Green leds: WHY?

sb_pete

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Please forgive me if this has been discussed before, but I have tried to search for it quite a bit and it has been nagging at me.

I see that the SF Kroma K2 milspec comes with four colors. I understand the use of red, blue, and IR, but what is the purpose of the yellow-green?

Is there some kind of military spec requirement for this color? Why?

Thanks all,
-Pete
 

Lightraven

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Probably works well with night vision goggles which are more sensitive to red and less to green. Maybe yellow/green is the optimum color.
 

Willabbott

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I've been told that Y/G is a NV Compatible color, and is also a good color for working with maps at night... supposedly it's more like white, in that colors appear more natural under it than blue or red, due to the fact maps don't use that color on them. Supposedly it's also a very bright color to night adapted eyes without making them not night adapted.


I can tell you from my 1 week worth of playing with my Kroma's (have both models still can't decide which I like better, but leaning towards MilSpec) that the Y/G is a great color at night... I haven't used it with fully night adapted eyes, however I've noticed if I wake up in the middle of the night it's plenty of light even inside the house, to see what I'm doing, and walk to the bathroom, etc... it's very dim in comparison to the red, and blue, which means less visible to others, less likely to ruin night adapted vision, etc.


I was told that NV Gear does not see Green or Y/G colors so that if you were to look past a buddies nvgear on his rifle, it wouldn't mess your unit up. I can tell you from trying it out, that at least on my Gen1 Unit this is not true... HOWEVER it is NOT very bright to the Gen1.

The Y/G appears through the Gen1 about as bright as the IR LED's (a bit more focused light) the Red/Blue Leds are much brighter through the unit. So I can say from experience that it may still see it, however it is definitely not as bright, of course it's not as bright to my eyes either. So it is VERY useful when working with NV gear, as it will not appear much brighter to your buddies than other IR sources around (low intensity IR sources, not high intensity) but will give you visible light to read a map, etc.

It is for sure not very much light, the Y/G A2's put out more light, however it's about the perfect amount of light to read a map, look inside a bag, and even see a few feet in front of you when walking.


According to resent reading I've been doing about human low-light vision, The part of the human eye responsible for seeing in low-light is most sensitive to blue-green so Y/G is fairly close to that color. There's some controversy about good colors at night, but the leading story I'm now hearing is that Turquoise (Blue/Green) is the best color for working at night, as it will not mess up night adapted vision as bad, but will give you what appears to be a brighter light source given the same amount of light, but that even white if used at low enough levels will not mess up your low-light vision as bad as a bright red source (traditional color of choice for night preserving vision).
 

DanielG

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I used a green or blue-green lens for pre-flight of the aircraft. Hydraulic fluid is red and you won't see it with a red lens.

ANVIS, or AN-AVS 6, goggles show the green lensed light as bright but it doesn't shut off the goggles. All lip lights, finger lights and other cockpit lights I've ever used are green based lens or LED because of goggles as well.

IR and red lens lights either are painfully bright or will shut off the goggles.
 

elgarak

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Willabbott is correct about the usage of Y/G: In military units with some personnel equipped with night vision and some without NV the ones not equipped use low brightness Y/G (as on the Kroma) to not interfere with the NV equipment.

With regards of night vision and color: The one and only color that has some usage for preserving night vision is low brightness red. Every other color messes with your night vision process.

Another problem with monochromatic light is that a lot of things you want to see are color-coded, and monochromatic light usually makes some color-coding hard to see, for instance on maps.

Unless you have special uses (military night vision with Y/G, dark adapted eyes with low red light, blood trailing/leak testing with blue), nothing in civilian life requires monochromatic light. You're ALWAYS better off with low brightness white.
 

RadarGreg

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Yellow-green also does not attract snipers. I was working on some equipment in Ramadi, Iraq and used my Kroma-MS while doing repairs on a radar. I needed a light that wasn't white(snipers like white light:faint:) and the red and blue washed out wiring colors and schematics. The yellow-green gave good, but not perfect, color rendition for the wires and color coded schematics. I was able to complete the repairs and other work under cover of darkness and didn't get shot. Well worth the money for me.:D
 

Lightraven

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Yellow-green doesn't attract snipers? Snipers like white light?

I'm sorry, I don't follow. I understand a sniper can't shoot what he can't see. But if he saw a target because the target was illuminating a yellow-green light, wouldn't he shoot him?
 

Daniel_sk

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I think that white light might be considered as enemy fire from distance? Emergency strobes for soldiers have blue filters because of this. Some "snipers" might shoot at everything that moves or emits a light... White light is also much more visible from distance...
 

Illum

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Yellow-green doesn't attract snipers? Snipers like white light?

I'm sorry, I don't follow. I understand a sniper can't shoot what he can't see. But if he saw a target because the target was illuminating a yellow-green light, wouldn't he shoot him?

assuming nighttime snipers uses night vision scopes....is there a possibility YG leds emit wavelengths outside of the night visions detection range?

might be a far stretch, but thats all I am able to think of given the information above:candle:
 

greenLED

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Check out my comments about Y/G in my A2 LED colors review thread for pics of the A2's Y/G LED's. In general, they're not terribly bright (compared to white), but they offer a good compromise in terms of color rendition (compared to other colors), as Greg very nicely indicated in his real world report (always nice to hear those).

The yellow-green gave good, but not perfect, color rendition for the wires and color coded schematics.


Unless you have special uses (military night vision with Y/G, dark adapted eyes with low red light, blood trailing/leak testing with blue), nothing in civilian life requires monochromatic light. You're ALWAYS better off with low brightness white.

I kinda agree with you elgarak. For most utilitarian purposes, white is clearly the most viable option. However, my experience with reviewing the Y/G A2 led me to believe that particular color is a close-second contender to white. I prefer the lower brightness of Y/G LEDs over white LEDs. Of course that's just my personal preference after playing with all those different LED colors.

For me, white A2 LEDs are too bright when I wake up in the middle of the night and turn those on. Y/G LED's, OTOH, are "just right" for me when I wake up in the middle of the night. Here's the catch, though, if your eyes not dark adapted and you turn the Y/G LED's on, they seem too dim for a few seconds. Then your eyes "catch up" and you can see well enough. This doesn't happen with white LED's - ie. you can go from an illuminated setting into a dark room and your eyes will "see" enough light if you use white LEDs.


Here's another catch, it depends on what light you're using too. Although the K2-M has 4 Y/G LED's, they're smaller than the 3 Y/G LED's in the A2. Thus, the K2-M's Y/G green is much, much dimmer than that of the A2. I don't have a light meter to give you a number, but the difference is very obvious when you compare them side by side.
 
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Lightraven

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If darkness is concealment, than any light reducing that darkness decreases the concealment and makes the soldier less safe. The intensity of that light (with some colors like green perceived as more intense by a retina for a given lux) combined with atmospheric conditions determine at what distance the light will be perceived.

So, if RadarGreg uses a white light that is just barely bright enough to see what he is working on (any dimmer and he couldn't), would using a yellow-green light of the same brightness (barely enough) be any less visible to an observer?

This is somewhat theoretical, since real white light flashlights are far too bright for stealth tactical use which is how I understood the reasoning behind colored filters. However, with the invention of really bright colored LEDs and lasers, I wouldn't want any good guys to think that they are safe solely because the light isn't white (one sniper target is the red glowing end of a cigarette--neither bright nor white). Only the HDS/Novatac series of flashlights have a safe white setting (the lowest on the basic/tactical models), in my opinion. I have an old Arc AAA with a nearly dead battery that is too bright.
 

DanielG

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If darkness is concealment, than any light reducing that darkness decreases the concealment and makes the soldier less safe. The intensity of that light (with some colors like green perceived as more intense by a retina for a given lux) combined with atmospheric conditions determine at what distance the light will be perceived.

So, if RadarGreg uses a white light that is just barely bright enough to see what he is working on (any dimmer and he couldn't), would using a yellow-green light of the same brightness (barely enough) be any less visible to an observer?

This is somewhat theoretical, since real white light flashlights are far too bright for stealth tactical use which is how I understood the reasoning behind colored filters. However, with the invention of really bright colored LEDs and lasers, I wouldn't want any good guys to think that they are safe solely because the light isn't white (one sniper target is the red glowing end of a cigarette--neither bright nor white). Only the HDS/Novatac series of flashlights have a safe white setting (the lowest on the basic/tactical models), in my opinion. I have an old Arc AAA with a nearly dead battery that is too bright.


I'll throw another monkey into that wrench.

Light is a primary way to see if someone's there at night, any light of any colour, of any intensity. Goggles pick up certain wavelengths better than others, just like the human eye. Green and blue/green can be invisible to goggles so you can have a higher intensity light in green than you ever could in -say- yellow or red both of which are picked up rather well by goggles.

Problem is that goggles are only part of what's looking for you. The other primary search item for me was a thermal sight. Look up OH-58D or go to the link in my sig and look at that golf ball on top. If you give off heat, it'll see you. You should see what someone with no grease paint on their face looks like under thermal, it's BRIGHT and stands out like one of these HID 35 watt lights on a moonless night. (didja like how I snuck flashlight stuff in there?)
 

RadarGreg

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Any white lighting in a combat zone is HIGHLY discouraged, even a dim one. I didn't have a Gatlight with infinite adjustability handy, and the Kroma on even low white seemed too bright to me. This was an area of Ramadi where snipers were getting 800 meter headshots, and I didn't want to test the theory that the low white was dim enough to be safe. A SEAL team later took out the sniper, but they didn't think to tell me if the sniper had a night vision scope.:whistle:

The yellow-green is a good compromise and is difficult for some night vision devices to see. Red LEDs, even on a low brightness, wash out colors on wires and schematics. Same thing for blue LEDs. I wasn't doing bomb disposal work (cut the blue wire...no the red wire!), but was working to get a radar system back online. Having the Kroma-MS helped me get the work done, and be able to post about it here.
 

Patriot

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assuming nighttime snipers uses night vision scopes....is there a possibility YG leds emit wavelengths outside of the night visions detection range?

might be a far stretch, but thats all I am able to think of given the information above:candle:

I don't own any yellow/green leds myself, but I do own some yellow and I do own a couple of greens...Both of which show up like blazing sun-light. It's bright enough that protection circuitry kicks in on my genII viewer.

Maybe Surefire is just using yellow/greens because like RadarGreg said, "the military is highly discouraging the use of white light" and it happens to be more utilitarian than red or blue? ..... not sure.
 
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Lightraven

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The Army of 1992 and my agency's tac unit of 1998 was very much against white light and, in favor of red--if you had to use a light at all, which was certainly discouraged to the extent that I asked a tac unit instructor what he thought of exposed tritium night sights. In retrospect, I don't think exposed night sights were a problem.

We used ponchos to throw over the light, cup our hands over bezels to narrow the beam, use green chemical light sticks with those holders with the closable windows, write info in grease pencils on green glow in the dark material--anything to minimize light emission in hostile territory (training purposes).

Light amplification technology has drawbacks that experienced people could exploit, though using a particular type of light is certainly not among those drawbacks.

Evading thermal imagers can be tough. I can see a bird in a tree at 1 mile away. I can identify people I know at a few hundred yards and whether they are wearing a bulletproof vest under their clothes. Most of those who manage to evade thermal don't realize they are doing it. As of about 7 years ago, the Navy SEALs here hadn't figured it out yet! Sorry guys!
 

Willabbott

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I find this discussion very interesting...

I'm curious has anyone thought about asking Surefire what their opinion is of that color, what reason they give for it's use?

I thought about emailing our rep today but didn't, perhaps I will tomorrow, just act like I have a customer asking, and I don't know what to tell them (I work for a decent sized Surefire Dealer)

For an interesting read: http://stlplaces.com/night_vision_red_myth/
I'm not sure if it's factual or not... It's an interesting read none the less...


I do really like the Y/G I'm with GreenLED it's quite a bit of light to see with, but very dim in comparison with other colors.

The Y/G does seem to preserve colors pretty well while being lower signature than the white.

Y/G is definitely not overly bright to a Gen1 Night vision Device

For me the Milspec is proving to be very useful... I'm not military however I'm working with NV more and more often, and the IR is used occasionally there, the Y/G is slowly becoming my primary working color at night... and I also work with firearms training, and we use plastic training rounds during night fire courses which are much easier to locate with the blue... in fact I'm starting to find the Red the least likely used color.


I may go ahead and email our rep at SF tomorrow, and see what they have to say about the color, just for the heck of it.
 
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