Filter Colors for Night Vision and Body Fluid Identification

Nephron44

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Hey everyone!

I will be starting a tactical medic course next week, and I am wondering what color filter would be best.

I use a Streamlight Strion as my main light, and I can get a filter in red, green, or blue. I want a color that preserves natural night vision (we won't be using NVGs), but also allows me to identify body fluids (mostly blood) of a casualty. I can't use normal bright white because it can backlight the team, making us all a target.

What color should I choose?

Thanks!
 

Keitho

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Unfortunately, your two goals, identifying color accurately, and preserving night vision, are at odds with each other. Red light will preserve foveal vision best, while high CRI white light will allow best identification of colors. Intensity of light will prevent or cause you to be seen by aggressors.

So for medical use, I'd go with a high CRI white light that defaults to moonlight mode, like the nitecore mt06md (even that might be too bright for tactical situations at 4 lumens). For reading a compass and other covert activities, use a red filter and low intensity.
 

Nephron44

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Unfortunately, your two goals, identifying color accurately, and preserving night vision, are at odds with each other. Red light will preserve foveal vision best, while high CRI white light will allow best identification of colors. Intensity of light will prevent or cause you to be seen by aggressors.

So for medical use, I'd go with a high CRI white light that defaults to moonlight mode, like the nitecore mt06md (even that might be too bright for tactical situations at 4 lumens). For reading a compass and other covert activities, use a red filter and low intensity.

Thanks for the info! I don't necessarily need to have good color identification, but I basically need to be able to determine if someone's clothing looks wet or not. If there is a casualty and his shirt looks wet in the dark, I don't care what it is...his shirt is getting ripped open to check for a wound. I just need to be able to identify if someone is bleeding or not.

Thanks!
 

iamlucky13

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Does your course instructor or anybody you might know how has taken the course before have a recommendation?

If this is a military or perhaps even a police course, I'd have thought they'd already have a standard type of light.

Generally, monochromatic light is not great for picking out subtle contrast differences or telling what colors objects are, but generally you want to have lights similar to the colors you need to see. That makes me lean towards red for medical purposes. You eyes do have best sensitivity to green light, and astronomers seem to debate between using the traditional red vs. green. In either case, keeping the intensity low is important to avoid affecting your night vision, but if you need a higher intensity in order to have the acuity to perform detailed tasks, I'm pretty sure red ends up working better.

Not blue, however. If I'm remembering right, your eye is most sensitive to blue light in your peripheral vision, but has very low sensitivity to blue in the central vision. So blue light could be the most likely to attract attention, yet least helpful to accomplish your medical tasks.

I just checked the specs on the Strion. 65 lumens on low is really bright for night vision situations. That also makes me more inclined towards a red filter, which means both reducing the effect on night visions, and because LED's are usually weak in red light, significantly reducing the final output past the filter.
 

Chad Varnadore

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I have to assume yours is a military application, as in civilian law enforcement medics never approach until the area has been cleared of any threat by law enforcement, and despite first responder training, police pretty much never treat wounds, as they have too many other responsibilities, including clearing a way for EMS. We were even discouraged from doing basic CPR when I went through BLET as good Samaritan laws didn't apply to law enforecement. If it is military, don't they have a list of approved lights, like they do with most things? From what I've seen all branches of the US military have very tight regulations on non-issue items that can be carried or worn.
 

bykfixer

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Not trying to be humorous here:
An incan Mag Solitaire would provide a good way to ID the things you want to without giving away your position.

A green filter would be best for your current light. Notice what you see with NVG is green tinted....

I agree with the others that the instructors likely know what to use and will give you that info in class.
 
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Nephron44

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I have to assume yours is a military application, as in civilian law enforcement medics never approach until the area has been cleared of any threat by law enforcement, and despite first responder training, police pretty much never treat wounds, as they have too many other responsibilities, including clearing a way for EMS. We were even discouraged from doing basic CPR when I went through BLET as good Samaritan laws didn't apply to law enforecement. If it is military, don't they have a list of approved lights, like they do with most things? From what I've seen all branches of the US military have very tight regulations on non-issue items that can be carried or worn.

My application is actually civilian law enforcement. More and more departments are adopting the care under fire model and are integrating medical professionals within their tactical teams, or are training tactical members in emergency medicine. This supposedly allows quicker triage and treatment of casualties, especially team member casualties. We don't do CPR or anything; it's basically stop the bleeding and get them out of there and to the paramedics on standby. The guidelines for civilian law enforcement TECC were adapted from the military TCCC guidelines.
 

Tixx

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What do the people running the course recommend?
 

jon_slider

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I think you should buy the whole set, Red, Green, and Blue

And then share what you learn…

Here is what a few Googles say about the applications of each color..

https://www.armytek.com/products/accessories/filters/

A Red filter has a larger number of applications. Some animals can't see red light so it's good for nigth hunting and is good for map reading because it doesn't disturb night vision. Flashlights with red filters are also widely used for signage.

A green filter is suitable for hunting and tactical use as a beam of green light can't be seen from aside and doesn't disturb a game.

A blue filter is widely used with various night vision equipment as well as navigation devices. Blue light is also perfect for reading chart and maps.


https://www.amazon.com/dp/B004ANZPCG/?tag=cpf0b6-20
• Red - Preserves Night Vision
• Green - Best Clarity Under Low Light Conditions,
• Blue - Easy to Trace Blood Trail

http://www.survivaledgelights.com/colored-flashlight-filters/
Red Filters
Red light does not detract from your night vision. That is why taillights are red. By using a red filter over your tactical flashlight, you can quickly read a map or get your bearings without destroying your night vision.

It has been one of the most popular choices to add as an optional filter.

Green Filters
Green light has a very narrow band. For that reason, it is often used for night hunting. Animals are not frightened by green light, and it cannot be seen from the side – only straight on. This makes it the ideal filter for your tactical flashlight when stealth is at a premium.

With the human eye being most sensitive to the green range of light this makes it an optimal color to use when traversing through the forest when you are using a low intensity.

Blue Filters
Blue filters are often used when reading maps or other writing because they cast black lines in stark relief against white paper.

One of the additional uses of blue filters is for hunters. Tracking wounded animals at night means picking up a blood trail. The blue light helps the blood stand out against foliage.
 

Nephron44

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I think you should buy the whole set, Red, Green, and Blue

And then share what you learn…

Here is what a few Googles say about the applications of each color..

https://www.armytek.com/products/accessories/filters/

A Red filter has a larger number of applications. Some animals can't see red light so it's good for nigth hunting and is good for map reading because it doesn't disturb night vision. Flashlights with red filters are also widely used for signage.

A green filter is suitable for hunting and tactical use as a beam of green light can't be seen from aside and doesn't disturb a game.

A blue filter is widely used with various night vision equipment as well as navigation devices. Blue light is also perfect for reading chart and maps.


https://www.amazon.com/dp/B004ANZPCG/?tag=cpf0b6-20
•Red - Preserves Night Vision
•Green - Best Clarity Under Low Light Conditions,
•Blue - Easy to Trace Blood Trail

http://www.survivaledgelights.com/colored-flashlight-filters/
Red Filters
Red light does not detract from your night vision. That is why taillights are red. By using a red filter over your tactical flashlight, you can quickly read a map or get your bearings without destroying your night vision.

It has been one of the most popular choices to add as an optional filter.

Green Filters
Green light has a very narrow band. For that reason, it is often used for night hunting. Animals are not frightened by green light, and it cannot be seen from the side – only straight on. This makes it the ideal filter for your tactical flashlight when stealth is at a premium.

With the human eye being most sensitive to the green range of light this makes it an optimal color to use when traversing through the forest when you are using a low intensity.

Blue Filters
Blue filters are often used when reading maps or other writing because they cast black lines in stark relief against white paper.

One of the additional uses of blue filters is for hunters. Tracking wounded animals at night means picking up a blood trail. The blue light helps the blood stand out against foliage.

Awesome info! Thanks!

If money was no object, I would get all three, but times are tight :/
 

Nephron44

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I ended up getting a red flip cap from Streamlight because given all the info, it seems like the most universal. I will report back after the class and let you know how it went!
 

Chad Varnadore

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My application is actually civilian law enforcement. More and more departments are adopting the care under fire model and are integrating medical professionals within their tactical teams, or are training tactical members in emergency medicine. This supposedly allows quicker triage and treatment of casualties, especially team member casualties. We don't do CPR or anything; it's basically stop the bleeding and get them out of there and to the paramedics on standby. The guidelines for civilian law enforcement TECC were adapted from the military TCCC guidelines.


That's interesting. Thanks for elaborating. If you're doing specialist/unit training, as another member said, green light is harder to see from the side - that is, any angle where you're not looking into the lights reflector. But unless the filter can be quickly flipped open, I personally wouldn't want it. Surefire has made some good flip open filters with spring hinges for their lights in the past, the spring hinges pop the filter out of the beam quickly and keep it there until you want it again. I don't know if they still make them or make them that way. With the trend in multi-mode lights these days, unless you're working with goggles or something I'd just get a good bright light that incorporates easy to access moonlight modes in the design. One moonlight mode may be optimal if it's the exact lumens you always will need, but I like how Armytek incorporates several levels of moonlight. With a light that has a good moonlight mode, then all you need to do is spend some time making the interface instinctive, which would be faster than even flipping the filter open, should you need to switch between bright and dim immediately. I would expect a moonlight mode, which is going to put out minimal lumens, but without distorting color perception, would be a better indicator of injury than any of the three common filter colors, and would likely be harder for someone to see than a much brighter light dimmed only by essentially a colored photo lens.

Instead of limiting yourself to one light, you might also consider getting a small secondary light for the application you've described - either a clip-on pocket light or a very small tactical light with belt holster. I've heard of a number of officers even carrying right-angled headband lights as a secondary light (not in the headband of course), which usually include at least one good moonlight mode well suited for low light applications like reading or working in tight spaces, which is one of their chief utilities. But many come with magnetized tailcaps allowing you to magnetize it on your car or most any metal surface to point in a specific direction. I'll often clip one to my belt, shirt pocket or vest. Even if I have a thrower in my hand, it ads nice augmented area coverage. It's utility is almost limitless, much more so than any conventional light. But it wouldn't replace a tactical light for duty carry.
 

ssanasisredna

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Unless you are using red light >650 nm, using RED has almost 0 benefit to your night vision. Most of the "use red" is based on bad knowledge and poor assumptions.

If you need light to see, you need light to see, period. If you need 1 lux, whether you have 1 lux red or 1 lux white they are both going to impact night vision. When you add in improved contrast, you can likely use a lot less white for the same visual acuity especially photopically measured.

The red for tail lights is not about night vision it's about what worked well with filtered Incan and glare.
 

eh4

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Unless you are using red light >650 nm, using RED has almost 0 benefit to your night vision. Most of the "use red" is based on bad knowledge and poor assumptions.

If you need light to see, you need light to see, period. If you need 1 lux, whether you have 1 lux red or 1 lux white they are both going to impact night vision. When you add in improved contrast, you can likely use a lot less white for the same visual acuity especially photopically measured.

The red for tail lights is not about night vision it's about what worked well with filtered Incan and glare.

I've heard both that red is better, and that equally low white light is just as good. What I've noticed is that I have less eye strain, and better central focus with low level red light, for instance when reading black text on white paper.
The explanation that I've read is that the central focal area of our eyes makes good use of red light for fine distinctions.
In a related note, it's been reported that blue light isn't as well focused on the fovea macula, that small central zone where we have the most detailed vision.
Whether that's true or not, it bears out with my experience of being able to see better with lower lumens of warm light as opposed to brighter, cooler lights.
I've never had the desire to try blue or royal blue light to compare with red, cool white vs warm was enough for me.

Finally, though studies are generally going to assume that everyone's eyes work the same way, it's entirely possible that different individuals have different limitations and advantages, especially at the edges of their ability to see, while being more uniform among subjects around the center of the bell curve of regular viewing conditions.
 
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ssanasisredna

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I've heard both that red is better, and that equally low white light is just as good. What I've noticed is that I have less eye strain, and better central focus with low level red light, for instance when reading black text on white paper.
The explanation that I've read is that the central focal area of our eyes makes good use of red light for fine distinctions.
In a related note, it's been reported that blue light isn't as well focused on the fovea macula, that small central zone where we have the most detailed vision.
Whether that's true or not, it bears out with my experience of being able to see better with lower lumens of warm light as opposed to brighter, cooler lights.
I've never had the desire to try blue or royal blue light to compare with red, cool white vs warm was enough for me.

Finally, though studies are generally going to assume that everyone's eyes work the same way, it's entirely possible that different individuals have different limitations and advantages, especially at the edges of their ability to see, while being more uniform among subjects around the center of the bell curve of regular viewing conditions.

There is some truth to a single wavelength being better focussed (and there being higher density of red photosites). There is also truth to perceived brightness of red being less, hence you probably would have been using far more red light versus white light if you were using your eyes as a judge of equal brightness. Reading black text on white is of course just one object recognition task.

The OP has an interesting requirement in both trying to identify substances (such as blood), something that typically requires color, and trying not to draw obvious attention (don't backlight the team). Specifically you are trying not to draw attention and that is going to be a factor of your environment. If the environment is lit with white streetlights, then white may be the least attention drawing, and a bright red spot (or light) will stand out. In an overall dark environment, white will create greater contrast, whereas red may get "sucked up" by the environment, i.e. pavement, vegetation.

It's always going to be a trade-off. You have to start off with what is the minimum acceptable amount of light, whether that be monochrome or white and work back from there.

To eh4's statement, a good tradeoff could be warm white (or maybe even very warm white). Blue is detected at far lower levels and in the peripheral vision at night. However, you may find the need for white to do your work. Very warm white mostly devoid of blue may be a good compromise. If you accidentally turn it on at high, it will create less glare for you as well (again, due to lack of blue).
 

Tusk

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The Streamlight Sidewinder has multiple color LEDs, is built military tough and shouldn't break the bank if you shop around. There are different models with different combinations of color LED's, including IR. I think it's the Sportsman model that has white, red, green and blue (no IR), so you can try them all.
 

iamlucky13

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Unless you are using red light >650 nm, using RED has almost 0 benefit to your night vision. Most of the "use red" is based on bad knowledge and poor assumptions.

If you need light to see, you need light to see, period. If you need 1 lux, whether you have 1 lux red or 1 lux white they are both going to impact night vision. When you add in improved contrast, you can likely use a lot less white for the same visual acuity especially photopically measured.

The functioning of night vision involves some rather complex chemistry, and it's taken me a while to get a genuinely better grasp of it than what we tend to hear passed around as common knowledge. George Wald, the researcher who figured out some of the key parts of the process, actually received a Nobel prize for that work. Here's a few pieces of what I have learned:

My understanding is you are correct that red light has no advantage - in fact a disadvantage - for seeing things in very low light. Our low light vision cells, the rods, don't perceive reds longer than about 640 nm at all, while our normal light vision cells, the cones, function to about 700 nm. The lumen and lux are defined based on our eye's normal light (photopic) sensitivity, and don't correlate properly to our low light (scotopic) sensitivity.

Red does, however, have an advantage for preserving the ability to see in low light when working in brighter conditions. Our low light vision via our rod cells has poor ability to discern fine details (acuity), so if you need better acuity such as for the classic example of reading an instrument panel on a submarine while still remaining able to see in minimal light in an emergency, you use red light to provide the higher resolution cone cells enough light for those detail oriented tasks.

The reason we lose our night vision when exposed to brighter light is the protein rhodopsin in our rod cells responsible stimulating our visual nerves undergoes a change in in response to light that make it far less sensitive to light. It's referred to as being "bleached." It then converts back to its sensitive state, but it takes time for all the rhodopsin in our eye to recover - usually half an hour or more. This is why our night vision continues to improve for quite a while even after our pupils are fully dilated.

But that change happens far more easily with blue light than with red light, so that especially with light beyond 640 nm, minimal bleaching occurs.

That's why I suggest if you need to do detail oriented tasks, but also retain your general night vision, go with a moderate brightness red light. If you just need to see with less precision what you're doing, a very low intensity green or white light is probably the best choice.
 
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eh4 mentioned that many studies assume that everyone's eyes work the same way. I have something to add in regards to color perception. Two years ago one of my eyes was injured. The injury was subtle, but resulted in the gradual development of a cataract. I had the occluded natural lens replaced with a crystal clear synthetic lens (it's an easy out-patient procedure). The result was astonishing: color temperatures as seen trough the synthetic lens were brilliant (think autumn sunlight at noon on a cloudless day), while color temperature perceived through my remaining "natural" lens were much warmer, like looking through champagne without the bubbles. I soon learned that both natural lenses had for years been been gradually yellowing as a normal part of aging...not anything to worry about just yet, but enough so that it caused me to reevaluate some of the lights I thought were too "green" or too "yellow" in their tint. In almost every case where I thought the light's color was "off," it turned out it wasn't the light, it was the ever-so-slightly accumulating warming of my natural lens that caused me to perceive the color as though seen through a glaze, or thin coat of varnish.

More relevant to this thread, I'm now able to resolve details at lower illumination intensity via the synthetic lens, than the natural lens. I can also see detail via the synthetic lens using moonlight modes less than one lumen, better than I can using just the natural lens. As a practical matter of course I use both eyes. And I know that eventually I'll elect to have the remaining natural lens replaced. For now though, the point of all this is to experiment to find a color temperature and intensity that works with the eyeballs (and natural lens tint) that you bring to the party.
 
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milehigher

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When your funds get straightned out i think its HDS that makes a dedicated tactical light to do what your want to do forensicaly, its a bit north of 250 for the light.
 
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