Do White and Colored LED's output UV?

I know this is probably a stoopid question but does a regular white or colored LED output UV?

Thanks!

Nope.

indeed.nope.

actually, for white LEDs, it actually depends on how white light is achieved..

some white LED (rare now) use UV light + a phosphor to output white light.. thus, some UV will get out.

most white LEDs use a royal blue LED combined with a phosphor now, though.

colored LED? nope!(well, unless it's a UV LED )

I think the blue ones may put out a tiny amount of UV, but not enough to be at all useful. That is why they make UV LEDs.

Thanks for the replies. I am mainly concerned with high power led's such as Cree XRE line. The reason I am asking is because in one of my applications I have a glass lens bonded to a stainless steel housing with epoxy right in front of my led's and I was told epoxy breaks down with UV light...do you guys think I will have a problem???

lightime said:

Thanks for the replies. I am mainly concerned with high power led's such as Cree XRE line. The reason I am asking is because in one of my applications I have a glass lens bonded to a stainless steel housing with epoxy right in front of my led's and I was told epoxy breaks down with UV light...do you guys think I will have a problem???

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After a few hundred years or so.

LukeA said:

After a few hundred years or so.

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Yeah, conservatively.

What if I need it to last 1500 years!!!...LOL...:laughing:

Ok so just to beat a dead horse and to be sure this wont be an issue I added a small drawing (I am terrible at drawing but hopefully this gets the point across)...so even if the epoxy is UV sensitive using it directly in front of high power leds of white and all colors there will be NO problems.....

Bump for any more responses....

Thanks

UV-A starts at 400nm. Even with Royal Blue LEDs there's nothing really going on below 440-450nm.

I'd be shocked if so much as a single photon of UV-A or anything below 400nm was emitted from these LEDs.

See for yourself, Spectra of low powered white LEDs : http://ledmuseum.home.att.net/specx18.htm

look at the blue LEDs.... radio shack makes a 5mm that puts out some UV below 400
http://ledmuseum.home.att.net/ledblu2.htm
you have to scroll down abou 1/3 the way through the page before you see the ones that do output
some UV. My rayovac 1AA blue LED fluoresces stuff

The radio shack LED does not put out UV. The output reaches baseline at about 420nm. What could be a bit confusing is that the baseline isn't subtracted in the figure.

space

The slightly more complex answer can be found in by looking at what the "real" LED mfgs do. They USED TO use epoxy as the encapsulant - low power LEDs still do. Now - virtually all power LEDs use silicones, because even the best epoxy could not handle the application.

There is quite a difference in power / heat level between your application and the materials in direct contact with an LED die, but - depending on how "sure" you need to be - as in "life or death" or "inconvenient".

If the project is really critical, then you can get more info from the material mfgs - they have a lot of experience actually.

Just as an example, while most white leds are backdriven with 460nm, quite a few are moving toward 450nm to increase color quality, etc. At 450nm, you can use them to "cure" UV epoxy and dental epoxy. It is definitely in the range to make an impact.

actually, i ve read somewhere that blue leds, when pulsed at certan hz, turn into uv leds, i'll try to find it, thou it was loong ago

Lynx_Arc said:

My rayovac 1AA blue LED fluoresces stuff

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i just noticed this the other night with partner's 1aa rayovac headlamp - the blue made the orange earplugs and a green lid fluoresce.
I wondered if that was part of why this was sold as a 'blood tracking' function (just that i think UV is used for forensic applications)

alpg88 said:

actually, i ve read somewhere that blue leds, when pulsed at certan hz, turn into uv leds, i'll try to find it, thou it was loong ago

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I think I remember seeing that article also, somewhere in a hobbyist mag I think. I believe they were talking about pulsing it at a much higher current than what could be used for continuous drive, and it shortened the lifetime of the LED rather severely. They were trying to get UV out of an LED in an era where UV LEDs weren't commonly available yet.

Linger said:

i just noticed this the other night with partner's 1aa rayovac headlamp - the blue made the orange earplugs and a green lid fluoresce.
I wondered if that was part of why this was sold as a 'blood tracking' function (just that i think UV is used for forensic applications)

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I think uv requires you to spray something to fluoresce the fluids I cannot remember the liquid but yes it does light up stuff a black light would normally do. Not sure that is in the UV spectrum but I have a UV light that does the same thing if that means much.

Lynx_Arc said:

I think uv requires you to spray something to fluoresce the fluids I cannot remember the liquid but yes it does light up stuff a black light would normally do. Not sure that is in the UV spectrum but I have a UV light that does the same thing if that means much.

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I guess you're referring to Luminol.

Calina said:

I guess you're referring to Luminol.

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yup datz da stuph