Uses for different LED colors

BigHonu

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I have noticed that LEDs come in some different colors and was wondering what applications/situations (other than decorative) these colors are used for.

The only thing I can piece together is that white leds are the best when color distinction is key but destroys night-vision.

So, what are the other colors used for, and in what situations? Are they practical for general illumination? I am most interested in uses for blue light, but am always open to gaining knowledge.

TIA and Aloha
 

Quickbeam

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White, like any other color, will destroy your night vision if it's too bright, but if it's dim enough, you're night vision will not be affected. Moonlight is white and yet doesn't destroy your night vision....

IMHO, the only reason to use any color other than white is for more light for navigation in the dark - some colors put out more light than others with the same power supply and therefore are better for simple navigation (walking around) in the dark. But regardless of what color you use (besides white) your vision is reduced to essentially "black and white" (or more accurately "monochromatic and white". Bad for just about anything except to keep from bumping into things.

Blue light is reported to be good for spotting blood droplets - for use by hunters and forensics teams.
 

Lux Luthor

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One thing to consider is that different colored objects reflect a given color differently.

As an example, just last night I compared a red LS to a PT blast (white) while shining through some brush. The Blast is a little brighter, but this application required seeing through green leaves. The white reflected off the green leaves brightly, but the red did not. So the white lit up the foreground, but not the red.

The red allowed me to penetrate the brush better than the white, despite being a little dimmer. I could simply see further through the brush with the red than with the white! This kind of effect is small when using a typical 5mm LED, but with an LS it's quite noticable!

So as a general principle, I would say that colors are useful when you have a myriad of different colored objects in your landscape, and you want to accentuate certain colors, and not others.
 

BigHonu

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Thanks Quickbeam.

So brightness is a factor to use another color.

What about blue light? I only ask because it seems to have a low lumen output (based on Lumileds measurements on their LS page) but in all the pictures I have seen (of the different LS colors), it is much brighter in comparison to white. I apologize if I am using the wrong terms to describe the light. Still trying to learn.

Aloha
 

Quickbeam

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I believe the blue led light will always appear "brighter" than a white LED for the following reasons:

The white LED really is a blue LED with a phosphorescent compound coating the light producing die. When the blue light hits the phosphorescent compound, it is absorbed and re-released in a number of different frequencies, some of which the eye is less sensitive to than blue.

The blue LED releases all of it's light in a (nearly) single frequency. Since all of the light is in this one frequency, as opposed to spread out over the whole spectrum which includes some colors we are less sensitive to, the blue appears brighter to our eyes.

Somebody can chime in and tell me if I have this wrong, but this is the way I understand it.
 

Quickbeam

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Lux -

That makes sense - the leaves absorb red light (that's why they look green - they're reflecting the green), so you wouldn't get distracting reflection off the leaves very much at all, allowing you to see the background better. Neat!
 

axolotls

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I modded my mini-mag with that super bright green led. It's really bright, but not that useful in the dark.
 

EMPOWERTORCH

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The different colours of LED's have differing uses. Astronomers have red torches to preserve thier night vision. We've all seen those movies about submarines where they "switch to red" to allow for better viewing of periscope images.
Orange and "neon coloured" LED's are very efficient these days. Thier chemistry enables them to be iused with fewer battery cells.
Green LED's make wonderful walking torches, as I found out whilst testing my BT1 prototype this weekend. The colour is easy on the eye and lit up the countryside nicely. It is pretty obvious that green vegetation is going to reflect light from torches with this colour light really well! Reading using this colour light was also a pleasure!

Cyan LED's are the most efficient both in terms of photons per watt and visual response. The light is closer to natural light such as found on a summer's evening. Nichia make 5mm cyan LED's with very high mcd figures. The 5w cyan Luxeon star LED is possibly the brightest solid-state light source in the world. I eventually want to get hold of one of these and install it in my floodtorch. Colour rendering is better than with a primary colour LED.

Blue and beyond
Blue LED's are used in torches by the military and by aeroplane pilots.

UV LED's
Ultra violet makes cedrtain substances fluoresce and could be very useful in detecting fake bank notes. Most British currency notes have a fluorescent watermark which shows up in UV.
I've already had a request for a BT1 torch with UV. The LED's are rare and very expensive at the moment. I may have BTx series torches made with both visible and UV LED's and a dual switch system. The BTx system is so adaptable that way!
 

BigHonu

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Thanks to everyone for their responses. I have never owned a LED color other than white so this information is really helpful in making future purchases.

Aloha
 

lambda

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