Purpose/experience with blue and green LED

jellydonut · Sep 19, 2010

Hey guys

I see some lights have blue secondary/tertiary LEDs - namely the white/blue SF A2, and the SF Kroma.

From reading threads here I've learned that blue apparently makes blood glow fluorescently - does anyone have any photos and/or hands-on experience with this? I'm just wondering what the use cases for blue is..

It might be something else I need even though I don't need it at all, like UV and IR.:nana:

While I'm at it I guess I could ask what on earth the purpose of kermit green LEDs are, like the ones found on the Kroma Mil-Spec and the A2 white/green.

Anyone?

B0wz3r · Sep 19, 2010

This is a great question and something I've always wondered about myself.

I've heard that blue light is supposed to make blood stand out, but it doesn't make sense that it would make it glow or fluoresce.

Because of how subtractive color mixing works, objects only reflect wavelengths that correspond to the color we see the object as. In the case of blood since it appears red it should only be reflecting longer, red, wavelengths back and absorbing everything else. So in this case, I would think blue light would make the blood appear black and shiny, like tar, rather than fluorescing. Of course there may be other substances in blood that have an effect, but just off the top of my head and from what I know about color perception I'd say blood should look black under a blue light.

jellydonut · Sep 19, 2010

Okay - I might just have misunderstood what people were saying. Either way blue light is apparently supposed to make it easier to see blood. I've skimmed through a bunch of mammoth threads and there seems to be divided opinions on that as well.

However, Surefire offers blue and green LEDs and they're not known for manufacturing gimmicks. I've shot a question to them about these colored beams, their purpose and target market, but I'm sure someone here knows as well.

LumensMaximus · Sep 19, 2010

Blue LED's would be used in forensics for spotting blood at crime scenes, hunters may also use at night for tracking wounded animals, not sure about green...

mcnair55 · Sep 19, 2010

Have a look at this kit,it gives details for what each light and filter is for.

Wolf Eyes Forensic Light Sources Kit.

hotlight · Sep 19, 2010

green- less visible to NVGs, or not as harsh to person with NVGs on.
better than red when using maps while trying to preserve night vision
read somewhere-pilots use green instead of red in cockpits(at night) to see instrument readings better? and to read maps easier.

Pacecar · Sep 19, 2010

Good article.

http://edcfeatures.blogspot.com/2006/12/on-leds-and-color.html

B0wz3r · Sep 19, 2010

Pacecar said:
Good article.

http://edcfeatures.blogspot.com/2006/12/on-leds-and-color.html

There's a problem with this article though... the color wheel they give indicates the three primary colors as being red/blue/yellow which is true for subtractive color mixture which is used for pigments, but incorrect for additive color mixture which is how light combines in colors. For light, the primary colors are the same as the different types of cone receptors we have in the retina, red, green, and blue.

Tally-ho · Sep 20, 2010

hotlight said:
green- less visible to NVGs, or not as harsh to person with NVGs on.
better than red when using maps while trying to preserve night vision
read somewhere-pilots use green instead of red in cockpits(at night) to see instrument readings better? and to read maps easier.

:thinking:
Green is the worse color to preserve night vision so there is probably an other reason for using green light by night in cockpits.
It is the most efficient light color (wavelengthes) for a night adapted vision.

Code:

Source: http://fr.wikipedia.org/wiki/Flux_lumineux

longboat · Sep 20, 2010

I remember when LEDs were first becoming popular for lighting purposes (flashlights, etc.). Green and blue were very popular because they produced the most light for a given amount of power used, likely because they were the native colors of the LEDs (no phosphor coatings). Maybe things have changed since LEDs have gotten much more efficient, but in the early years, green was the most efficient (yes, more efficient even than red in terms of output/mw). Blue just looks cool.

Surnia · Sep 20, 2010

Tally-ho said:
:thinking:
Green is the worse color to preserve night vision so there is probably an other reason for using green light by night in cockpits.
It is the most efficient light color (wavelengthes) for a night adapted vision

Green covers cone receptors for green colour perception, but the rods (night vision) also peak within the green wavelengths. This is why it won't preserve night vision, but it makes everything in green REALLY easy to see.

alpg88 · Sep 20, 2010

i use green leds in my mods, my purpose is; just for the hell of it.
green distorts colors thou, orange object looks dark blue in green light, also human eye is most sensitive to green, but in real world, i have not noticed much benefits of green,i have few green lights, lanterns, when we go camping i give them to kids to use, kids love it, cuz it looks cool and different, so do parents, the see where the kids are by their green flashlights.

Cataract · Sep 20, 2010

Supposedly green light will not scare game away.

Blue is supposed to help tracking. I'd like to hear form a hunter about that.
I doubt it would be of use for spotting blood, since both green objects (grass and foliage) and red, as in blood, turn black when lit by a blue light. Maybe it can help spot urine?

I read a post in here (can't find it anymore) where this guy had problems with coyotes or the likes and wounded one with his rifle. He tried a blue LED or filter to try and spot the blood trail, but said that he couldn't see squat, so he resorted to using just a normal flashlight. That's the only time I read anything about someone tracking an animal with a flashlight.

B0wz3r · Sep 20, 2010

alpg88 said:
i use green leds in my mods, my purpose is; just for the hell of it.
green distorts colors thou, orange object looks dark blue in green light, also human eye is most sensitive to green, but in real world, i have not noticed much benefits of green,i have few green lights, lanterns, when we go camping i give them to kids to use, kids love it, cuz it looks cool and different, so do parents, the see where the kids are by their green flashlights.

Actually, according to the textbook I use to teach sensory perception at the university where I'm an instructor, yellow is the color we're most sensitive to (Sensation and Perception, An Integrated Approach, 5th ed., Richard Harvey Shiffman, 2001, John Wiley and Sons).

While it's true that rods are most sensitive to wavelengths about 500 nm (green wavelengths) the combined response of the red and green cones produces more neurological activation in the visual system at the yellow wavelength of about 555 nm which is yellow. Further, rods are too sensitive to actually work at light levels at which normal color (photopic) vision takes place and are saturated and do not respond in that situation. Thus, if shown two lights of equal lux, one at 500 nm and one at 555 nm the 555 nm light will look brighter because there are more receptors being stimulated by that light.

Here's a link to a wavelength/sensitivity chart for the four types of photoreceptors in the retina so you can see the relationship of sensitivity to wavelength for each type of receptor. It is taken from the textbook I use to teach physiological psychology (Biological Psychology, 10th ed., James W. Kalat, 2009, Cengage Academic Publications).

http://s763.photobucket.com/albums/...on=view&current=Conewavelengthsensitivity.jpg

jellydonut · Sep 20, 2010

SF replied!

SF response said:
Dear [myname],

Thank you for contacting SureFire.

The blue LED's makes red colored fluids such as blood or hydralic fluid appear black under blue light. It is also is used for low light navigation, signaling and map/chart viewing in darkness which protects night adapted vision. The green LED is considered the closest brightness to white light while maintaining night adapted vision and is also NVG-friendly. We offer several color LED options for the A2 Aviator series flashlights since customers have different applications which may call for using either red, blue, green, yellow-green or IR in addition to a white light.

Best Regards,

Alex Nunes
Technical Support
SUREFIRE, LLC

my inquiry said:

Hello,

I've noticed that Surefire offers lights with secondary beams in various colors; the A2 with red, blue or green, and the Kroma with red/blue or green/IR on the Milspec model.

I can see the purpose with red and IR - preserving night-adapted sight, and for use with NVGs - but I have no idea what the use case for blue and green LED beams. I can't imagine Surefire offers colors just for the sake of it, so that's why I wanted to inquire as to the use case for these other colors. What is the purpose of these colors, and which customer groups buy these?

Best regards
[me]

Click to expand...

I've always heard that green is what our eyes are most sensitive to, and that red should be used for this purpose. We used red light for operations planning when I was in the military. (nothing hi-speed though, so might just be the navy pogues getting it all wrong..)

Well, now I'm all undecided. Maybe I should just get all colors and figure it out myself. Isn't that the standard answer?lovecpf

Yeah, I think I'll do that. White, blue, red, green, UV.:devil:

alpg88 · Sep 20, 2010

B0wz3r said:
Actually, according to the textbook I use to teach sensory perception at the university where I'm an instructor, yellow is the color we're most sensitive to (Sensation and Perception, An Integrated Approach, 5th ed., Richard Harvey Shiffman, 2001, John Wiley and Sons).

While it's true that rods are most sensitive to wavelengths about 500 nm (green wavelengths) the combined response of the red and green cones produces more neurological activation in the visual system at the yellow wavelength of about 555 nm which is yellow. Further, rods are too sensitive to actually work at light levels at which normal color (photopic) vision takes place and are saturated and do not respond in that situation. Thus, if shown two lights of equal lux, one at 500 nm and one at 555 nm the 555 nm light will look brighter because there are more receptors being stimulated by that light.

Here's a link to a wavelength/sensitivity chart for the four types of photoreceptors in the retina so you can see the relationship of sensitivity to wavelength for each type of receptor. It is taken from the textbook I use to teach physiological psychology (Biological Psychology, 10th ed., James W. Kalat, 2009, Cengage Academic Publications).

http://s763.photobucket.com/albums/...on=view&current=Conewavelengthsensitivity.jpg

thanks for the link, you thought me something new today, thou i wasn't far off, 555nm looks like unripe lemon.

btw it is very hard getting 555nm led, only 1 place has them, they call it green, guess it is certain shade of green,

Cataract · Sep 20, 2010

Thanks to the recent replies, this thread should be noted in a "threads of interest" of some sort

Tally-ho · Sep 20, 2010

B0wz3r said:
Thus, if shown two lights of equal lux, one at 500 nm and one at 555 nm the 555 nm light will look brighter because there are more receptors being stimulated by that light.

This is exactly what the table in message #9 shows, but it is not explained why. So it is because more cones (green and red) are stimulated that yellow appears brighter with photopic vision. With scotopic vision, it is green light that appears brighter to rods.

Code:

Source: http://fr.wikipedia.org/wiki/Flux_lumineux

Last week i found a web page (sorry, in french) where it is said that red cones are 4 times more sensitive than blue cones and there is a graph (on the right) showing the relative sensitivity of blue, green and red cones:

On the left graph, "bâtonnets" means "rods" and "cônes"... :sssh:

..."cones".

Code:

source: http://albators.free.fr/optique/couleurs.html

Mr Bigglow · Sep 20, 2010

For those of us who use red LEDs to preserve night vision, we know that red colours do not show up under red light. Blue is the most effective red-lighting primary colour there is and is therefore recommended for that. I've seen some blood under those conditions but don't remember it lighting up like a lightstick, just being easy to see. I have a Gerber light, name escapes me but like an Infinity with a little colour wheel, and besides the colour selecton thing, also find that red reaches out the least, green more, blue the most- until you get to regular white light. There was a thread asking for science-lab level 'proof' of some of this colour vs vision phenomena a while back- all I know is that is what my experience tells me. I'm trying to persuade someone to supply with Gen. 20 (or the most modern) night vision equipment, or perhaps IR vision equipment, but am confident I'll be using the Gerber for 100 changes of batteries... and the batteries last forever in that thing....

B0wz3r · Sep 20, 2010

Tally,

The claim about us being four times more sensitive to red than blue is true but not because of the properties of the cones themselves. Rather, it's because we have about four times as many red than blue cones. The retina encodes brightness by the amount of receptor activation it produces. Brighter lights produce more action potentials and more signal from retina to brain. Thus, for a red and blue light of equal lux, we will see the red one as brighter.

An interesting side effect of this is that under low enough levels of light, but not yet low enough for the cones to shut down and move us into scotopic vision, these perceived brightnesses reverse and we see blue as brighter instead. This is referred to as the Purkinje shift.

Another interesting fact is that we have no blue cones in the macula, only starting at the boundary of it so we don't actually see blue quite as well at the center of our vision.

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