Blue LED's, why ?

Why would you want to use Blue LED's, not UV, Blue ?

Blue is useful in forensics or in hunting.

Hunters use blue lights to follow a blood trail. It makes blood drops stand out as very dark nearly black spots against any background.

Mark

Flash_Gordon said:

Blue is useful in forensics or in hunting.

Hunters use blue lights to follow a blood trail. It makes blood drops stand out as very dark nearly black spots against any background.

Mark

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Is that really true or just hearsay.

I'm not a big fan of blue LEDs as they cause a lot more glare than other colors. They're hard to look at in the dark.

Blue LEDs are very bright. That's one reason. You probably know that white LEDs are really blue LEDs that have the dies doped with a phosphor so they put out a whitish light. Ma for ma more light will come out of the blue one because of the conversion losses incurred to make white. Compare the brightness of an old CMG Infinity with a blue LED (NOT the Ultra) to a CMG Infinity Ultra equipped with a white LED. The blue Infinity will be very close to the brightness of the white IU -- but it will have four times the runtime on a cell.

Blue light has traditionally been used in technical theatre because it is far, far easier to see with than red and yet it is a very easy color to mask from an audience. Often theatre techies with years of experience using low levels of blue light may routinely accomplish complex tasks that would be unimaginable to the uninitiated. Using any monochromatic light is a learned experience. There truly is such a thing as a trained eye.

It is often reported that blue light does not focus correctly on the normal retina -- which is true enough. It is also true that many with abnormal vision (glasses) may focus blue light on their retina's better than white light. I'm one who can read more easily with blue light than white light. The print looks sharper under blue light to my tired, old eyes because they are not normal eyes. There have been threads that have covered this.

Finally, Icebreak has posted on a few threads about hunting humans in the woods with Royal Blue lights. I would expect Icebreak to be along shortly.

Anyway, there are many uses for blue light although it's kinda like spill guys fighting with throw guys -- if you don't need it and haven't worked with it, it's easy to say it's useless.

Although I've spent years and years working with blue lights professionally, I'm really into blue/green for my everyday use. (see avatar)

They work well for those with near side ness, I know from experience. If you are far sighted like one of my coworkers who tried my blue inova light, it makes things blurrie.

I didnt try it, but wondered how successful it would of been to pull over someone when I had to drive a chevy montecarlo the silver model similar to the state cops if I had my blue light and flashed it out from the front window.

cobb said:

I didnt try it, but wondered how successful it would of been to pull over someone when I had to drive a chevy montecarlo the silver model similar to the state cops if I had my blue light and flashed it out from the front window.

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Depands upon your goals.

If you are looking for "3 hots and a cot" for a while followed by an assortment of dead-end jobs when you get out, then sure, it works pretty well.

Sub_Umbra said:

Blue light has traditionally been used in technical theatre because . . . it is a very easy color to mask from an audience.

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Sub_Umbra,

Why is blue easier to hide from the audience?

Scott

Color and vision is fascinating. To understand it and use it to one's benefit can bring rewards.

A long time ago ElektroLumens built a custom 5W cyan for me. It was the first single emitter flashlight that was documented at over 10,000 lux on CPF. It came in at like 12,720 lux even though it was resistored. I put a UCL in it and a stippled reflector. It's beam looks like a stage light but with smooth edges. It's on the green side of cyan. Annoys the crap out of humans. Causes some excellent edge finding in the woods. IOWs differentiates between shades of green and brown. IssacHayes has one that is more cyan than mine I believe.

I do think UV and NUV can be used to identify humans in the woods because they usually wear some kind of textile that will fluoresce. I mentioned this to Sub_Umbra. He let me know that some hunters use special detergent w/o phosphores. I still haven't come close to finding an excellent human hunter. My 5W RB does pretty well. PitBulls HID with 360nm passthrough filter looked pretty good. I can't remember which high-end HID comes with a passthrough filter but I'd like to see what that does. Of course a 5W 380 LED would be good but they don't exist.

Blue can be used for many things. If you are trying to read the print on a chip hidden in a dark computer the print will stand out.

I'm not a hunter so I don't know that blue won't work for blood tracking but I've done tests that indicate it doesn't do much. I do believe red can be used to find blood. Xenopus' blood tracker looks like it would work and it makes sense. I would like to see a light that strobed between blue and red. That might work very well.

Here's a discussion about LED light frequency and vision correction.

If you want to know a lot about light and vision here's a link Canuke gave us with several pages of well laid out information including graphics: Light and the Eye.

Sidebar for Sub_Umbra:

I went ahead and ordered a Terralux Cree UV (395nm I think) and a PR holder thinking it might work in a Mag2C. I don't think the Mag reflector is going to work exceedingly well. Newbie says that you need a deep "banana tip" to get much throw. I've never seen an Aleph19 but apparently it does pretty well.

Post #9 in this thread.

beezaur said:

Sub_Umbra,

Why is blue easier to hide from the audience?

Scott

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I can't give a scientific reason. From a practical side I can say that most of the time when we wanted to hide light from the audience we would use some type of black fabric with a nap. On the cheap end it would be something with a very fine nap, typically black Commando Cloth. If one had a bigger budget something with a deeper nap like a black velvet could be used and the deeper the nap, the less light will be reflected by it.

IMO whichever fabric is used the 'splash' from a blue light is much easier to soak up than the splash from a white light. As I said, I can't give any scientific explanation for this but most theatres I've worked in seem to operate on the same principal. I've seen a number of examples of white light hitting black velvet where the black velvet looked absolutely, positively, stark raving white from the audience and had to be dealt with to 'knock it down' one way or another. It sounds impossible but it does happen -- and sometimes it can be almost breathtaking. Mildly similar things can happen with blue light but they aren't nearly as severe or extreme and may always be dealt with in a simpler fashon.

I'm sorry that's all I've got. I hope it makes things clearer.

Cool. Thanks, that does explain it a lot.

Now I have use for 3 of the 4 colors in my soon-to-be-shipped (I hope) SureFire Kroma "milspec"

Scott

Sounds great. Living in an apartment aint so great when you are more of a prisoner inside and trying to feed the visious cycle of earning money to buy food.

That would solve a lot of my problems, including no health insurance.

beezaur said:

Depands upon your goals.

If you are looking for "3 hots and a cot" for a while followed by an assortment of dead-end jobs when you get out, then sure, it works pretty well.

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Sub_Umbra said:

IMO whichever fabric is used the 'splash' from a blue light is much easier to soak up than the splash from a white light. As I said, I can't give any scientific explanation for this but most theatres I've worked in seem to operate on the same principal. I've seen a number of examples of white light hitting black velvet where the black velvet looked absolutely, positively, stark raving white from the audience and had to be dealt with to 'knock it down' one way or another. It sounds impossible but it does happen -- and sometimes it can be almost breathtaking. Mildly similar things can happen with blue light but they aren't nearly as severe or extreme and may always be dealt with in a simpler fashon.

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Sub, thanks for the explanation. I've always wondered why blue was the preferred color for "lampies" working in theater.

Here's a little story about me and a blue Orb.

https://www.candlepowerforums.com/threads/122817

I would guess that blue is easier to hide from the audience because of Rayleigh Scattering.
It's the reason that the sky is blue during the day. The blue photons from the sun are more easily scattered from their initial path and "bent" toward the surface of the Earth.

Thus, at a distance, the blue light looks dimmer than the exact same power red light because the blue photons spread out faster the further you get from the source.

cobb said:

They work well for those with near side ness, I know from experience. If you are far sighted like one of my coworkers who tried my blue inova light, it makes things blurrie.

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Hmm, that ought to be the other way around.

Blue light refracts at a slightly sharper angle than does red. This means that it focuses to a point closer to the lens than does red.

If you focus your eyes on a nearby object and there is a white light in your field of vision that is farther away, that light will have a blue fringe. Because your eyes are focussed on a nearby object, the distant light is seen as someone who is nearsighted will see it -- the blue component is making a bigger blur than the other colors. All the light from the faraway light is focussed in front of the retina, with the blue light focus point being nearest the lens/farthest from the retina.

If you look at a faraway object and have a small white lightsource nearby in your field of vision, that lightsource will have a red fringe. This is because red, refracting the least, will focus farthest away from the lens, which in the case of an object too close, means farthest behind the retina. It also means that in this instance, blue is closer to its focus point. For farsighted people, most objects are "too close", so the red end is the blurriest.

Another quick way to see this in action is to take a simple lens/magnifying glass with a longer focal length (>100mm; don't use a camera lens as they prevent color separation, aka chromatic aberration, by design) and focus the image of a compact white light source. You will find that if the lens is too far away from the paper, the blur has a blue fringe; if it's too close, the blur fringe is red. (Anybody who liked to fry things with a magnifying glass as a kid might remember that the most burning power came with a bit of a blue fringe around the image of the sun, as red and infrared are the brightest parts of sunlight, and gave the most heat in focus.)

So, what this means is that for farsighted people, blue light is closer to focus than red; for nearsighted people, it is red light which is sharper. Given this, however, there are many more red and green cones than blue, so red's benefit for nearsighted people is probably more pronounced than blue's for farsighted folks.

If you wear glasses, a prescription that is a bit stronger than you need will reverse this effect.

MicroE said:

I would guess that blue is easier to hide from the audience because of Rayleigh Scattering.
It's the reason that the sky is blue during the day. The blue photons from the sun are more easily scattered from their initial path and "bent" toward the surface of the Earth.

Thus, at a distance, the blue light looks dimmer than the exact same power red light because the blue photons spread out faster the further you get from the source.

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I don't think that rayleigh scattering is noticeable at the smaller scale of a theater.

What I suspect is the case here, is that blue is the least obtrusive color, both perceptually and psychologically; it is usually associated with background elements or backdrops in design, possibly because in nature, blue is most strongly associated with distant, big things, such as skies and oceans. When solid-colored graphic elements are mixed, blue tens to be seen as farther away or "behind" the other colors.

This is probably due to the fact that we are least sensitive to blue (in conditions of photopic "daytime" vision), in part because of a yellow tint to our eye lenses, which deepens with age.

My cyan is bluer than most lumileds luxeon cyans. It's true cyan like 485 nm argon laser colored.

It's very bright to the eye, even though the lumens are less than a white flashlight, it looks brighter.

Blue leds, well everyone else explained it already. I'd prefer UV over blue in the kroma any day though!

I guess we will see more blue LEDs torch running around. Can we fit some in the Maglite?

nsx88, it is possible to fit a luxeon I onto the terralux drop in for minimags.

just unsolder the white luxI and solder the blue one IN!

make sure you got the "+" and "-" correct. or you will end up with a toasted blue luxI.