# Do White and Colored LED's output UV?



## lightime (Sep 23, 2009)

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

Thanks!


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## blasterman (Sep 23, 2009)

Nope.


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## csshih (Sep 23, 2009)

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 )


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## Lynx_Arc (Sep 23, 2009)

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.


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## lightime (Sep 23, 2009)

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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## LukeA (Sep 23, 2009)

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???



After a few hundred years or so.


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## bshanahan14rulz (Sep 23, 2009)

LukeA said:


> After a few hundred years or so.


 
Yeah, conservatively.


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## lightime (Sep 23, 2009)

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.....


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## lightime (Sep 24, 2009)

Bump for any more responses....

Thanks


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## blasterman (Sep 24, 2009)

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.


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## Calina (Sep 24, 2009)

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


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## Lynx_Arc (Sep 24, 2009)

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


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## space (Sep 25, 2009)

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


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## HarryN (Sep 25, 2009)

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.


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## alpg88 (Sep 25, 2009)

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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## Linger (Sep 26, 2009)

Lynx_Arc said:


> My rayovac 1AA blue LED fluoresces stuff



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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## PhotonWrangler (Sep 26, 2009)

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



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.


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## Lynx_Arc (Sep 26, 2009)

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)



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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## Calina (Sep 26, 2009)

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.


 
I guess you're referring to Luminol.


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## Lynx_Arc (Sep 26, 2009)

Calina said:


> I guess you're referring to Luminol.



yup datz da stuph


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## 2xTrinity (Sep 27, 2009)

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.


Many fluorescent dyes will be activated by blue light as well as by UV light. For example, the dye in yellow highlighter ink will glow quite brightly from blue light. The dye from orange highlighter ink will even fluoresce if exposed to green light (hitting it with a green laser, you can see a distinct yellow color).

The advantage of using UV for fluorescence is because it is not visible, it is more easy to see the fluorescence taking place than when you illiminate it with blue (itself visible, thus reducing the contrast or ability to see the fluorescent dye).

So the fact that you can see fluorescence from a blue/white LED does not at all mean it must be releasing UV radiation.


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## billw (Sep 27, 2009)

"Fluorescence" as a phenomenon does not require ultraviolet light. It just means that light of one frequency is absorbed, and a different frequency is emitted. Excitation by UV invisible to the human eye and emission in the visible spectrum is particularly interesting because the the "magic" factor, and because it permits "brighter than natural" appearances (a fluorescent red paint in sunlight will emit more red light than there exists in the sunlight incident upon it, which is presumably why it looks so strange.) But it would be equally proper to label something that absorbs green and emits red as fluorescent...

As for the original question, damage of epoxies by UV is probably something that depends on the energy of the photons, so it's not unlikely that blue light will damage epoxy eventually; just slower than UV. Perhaps MUCH slower. I'd be more worried about the heat. (and I suspect that the reason that silicones are used in modern LEDs has more to do with their thermal properties than UV resistance.)


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## lightime (Sep 28, 2009)

Thanks very much for the replies and all the info. Very much appreciated.


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## Mark in Upstate NY (Jan 10, 2014)

Hello eveyone,
The flash led bulbs on my new LG G2 smart phone cause our uranium glass objects to flouresce brightly.

Could one of you explain this to me, please?

Thanks and kind regards,
Mark


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## PhotonWrangler (Jan 10, 2014)

Mark in Upstate NY said:


> Hello eveyone,
> The flash led bulbs on my new LG G2 smart phone cause our uranium glass objects to flouresce brightly.
> 
> Could one of you explain this to me, please?
> ...



While LEDs use either blue or near-UV chips in them. There is enough blue energy in the white light to excite fluorescent objects including uranium glass. I've noticed that blue LEDs will fluoresce a number of things.


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## WhiteRabbit (Sep 26, 2014)

I purchased some 5050 LED's from Amazon just recently. http://www.amazon.com/gp/product/B00F6RC4JC/?tag=cpf0b6-20 described as white, though IMHO that label doesn't really fit. To my eyes, they appear more like "light purple" than white, and the photo even seems to demonstrate that:








I started by driving it at very low voltage and low current just to verify that I had the polarity right before cranking up the power. In doing so, I noticed that the phosphor coating had definite "holes" in it where emissions seemed to be getting through without converting through fluorescence. Maybe they were "thin spots" where the phosphor was unusually thin rather than holes. Or maybe it was both. I'm not an expert, so I can't say for sure. However, maybe it does explain the obvious purplish appearance?

These LED's didn't come with a datasheet, and I have no idea who makes the actual LED dies. *Bottom line: though this thread is re-assuring, I want to do my own testing to convince myself that there's no UV "leaking" through. *Not just for these LED's pictured above, but for any LED's and LED bulbs/fixtures I might get in the future too. Would a sensor like one of those below be of any practical value in settling the matter? 





http://www.adafruit.com/products/1777

In looking at page 15 of the datasheet (http://www.adafruit.com/datasheets/Si1145-46-47.pdf), the sensor seems much more sensitive to UV-A than UV-B, though. If I'm reading this thread right, if there were any UV (which most of you are saying there isn't), it would be in UV-B rather than UV-A. Right? So, would this sensor be of any use at all, or would I be better off looking for something that can detect UV-B?

So, maybe this analog sensor would be better?





https://www.adafruit.com/products/1918


Looking on page 2 of this analog sensor's datasheet ( https://www.adafruit.com/datasheets/1918guva.pdf), the wavelength response seems more shifted to the right. However, I'm not good at reading data sheets, and so I'm also unsure as to whether in absolute terms it is more sensitive or less sensitive than the digital sensor above. 

Sparkfun has a different analog UV sensor: 




https://www.sparkfun.com/products/12705

Looking on page 4 of its datasheet (https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/ML8511_3-8-13.pdf), the spectral response curve looks more uniform. So, shooting purely from the hip, I'm leaning toward the sparkfun analog sensor, even though in general my preference would be for a digital sensor (like the first one above) rather than an analog one.

*So, any advice or consensus on UV sensor selection for the stated purpose? Maybe there's a better one I haven't linked to here? * If there's interest, I could post the measurement results. I do want a sensor that's on a breakout board rather than just raw die, as that will make it easier to use, even though it narrows the consideration set.

Is it safe to rule out UV-C as a possible factor? It does not appear that any of these sensors are sensitive to UV-C.

By the way, has anyone here already tried doing UV measurements? If so, how did it go?


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## WhiteRabbit (Sep 26, 2014)

In case anyone's compacent, it appears that at least some white LED's *are *driven by UV. The following excerpt is from the Philips website (link to source provided below):

UV LED with RGB Phosphor: White LED can also be made by coating a UV emitting LED with three different phosphors capable of emitting red, green and blue light respectively. See figure below. The principle of operation is analogous to that of fluorescent lamps. The resulting white light has excellent colour rendering properties.


Pros: Excellent colour rendering, since white point is determined by phosphors only, there is no change in colour temperature due to a change in current.
Cons: The UV light degrades many materials used in packaging the LED including epoxy and hence shorter lifetimes. This method is less efficient than using blue LEDs with a yellow phosphor coating. *It is conceivable that a faulty LED could possibly emit levels of UV in excess of safe limits. * [Note: Bolding added by me, WhiteRabbit]





http://www.lighting.philips.com/pwc...versity/internet-courses/LEDs/led-lamps5.html

IIRC, UV excied phosphor is the mechanism underlying the Philips Calculite LED lighting fixtures: http://www.lightingproducts.philips...olier USA/pdf/Calculite White LED catalog.PDF
I'm unsure whether current generation calculites are that way, but again, IIRC, that is how version 1 worked not long ago, around the time this thread was originally started.


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## PhotonWrangler (Sep 26, 2014)

Well Philips is claiming that they cooked up UV-excited white LEDs in 2009 but G-E was experimenting with their "VioLED" technology in 2007. I even toured their R&D plant and saw some prototypes. I remember that the phosphor blending machine reminded me of a carnival cotton candy machine with spatters of product on the glass walls. 

There's an old thread on G-E's product here.


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## SemiMan (Sep 26, 2014)

lightime said:


> 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.....



Many epoxy compounds will yellow under high levels of blue, not just UV.


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## ER1C (Sep 26, 2014)

blasterman said:


> 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.



Good to know! Thanks!


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## WhiteRabbit (Oct 3, 2014)

The sparkfun sensor looked like it might false positive for UV on blue light, so I ordered the adafruit analog sensor above (GUVA-S12SD) instead. The GUVA-S12SD will false negative if there's UV just below 400nm, but it's sensitive only to UV and shouldn't false positive. BTW, none of the sensors are sensitive to the UV-C range. So, it won't by any means be a perfect test, but it's the best effort I'm prepared to undertake given limited time and resources and the absence of any suggestions or feedback regarding UV sensor selection.

It's completely unrelated, but I'm also going to attempt to measure any flickering which may be present, due either to PWM, voltage ripple, component failure, or whatever else. Studies of industrial workers suggest it can cause eye fatigue and other negative consequences, even if the exposure is below the level of conscious awareness (which, if true, makes it pernicious). It correlates to dose and duration, and in a residential environment you might have a lot of both dose and duration, depending on the specifics of your lighting. Anyway, I merely mention it as an aside, as it's outside the main topic, which is UV. Anyhow, look it up if you're interested. In the US, as near as I can tell, no one in government is monitoring this stuff at all--just energy efficiency, if that.


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## PhotonWrangler (Oct 3, 2014)

Take a look at Craig's LED Museum site. He did a _huge_ amount of spectral analysis of LEDs from UV to IR. The answers you're seeking are there. Scroll down the left hand frame to the LED wavelengths you're interested in.


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## LEDMaster2003_V2 (Oct 9, 2014)

I have this little “weaponlight” that came with an Adventure Force pistol, it uses a deep (probably royal) blue LED, and it did _slightly_ darken my Transitions® lenses (after about 10 seconds), so it was putting out some UV.

http://www.swap.com/item/adventure-...WPXXshQw9ckVU_gTq7HZGN8Zgb6iJZuqHQhoC2rTw_wcB

I think the current ones have white LEDs though.


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## SemiMan (Oct 9, 2014)

More likely your transition lenses have some blue sensitivity


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## PhotonWrangler (Oct 9, 2014)

Most photochromic lenses are designed to activate in the UV range of 320-400nm. This is why they don't activate behind car windshields which block these wavelengths. There is a new formula for photochromic lenses that is being marketed as Transitions "Xtractive" that will activate at longer wavelengths in the blue-to-NUV range.

More info on photochromic lenses here.


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## The Led Machine (Oct 11, 2014)

Apparently it does emit UV either be white or colored though it's just a tiny amount.
Link for referrence: http://www.leapfroglighting.com/lighting_and_uv_radiation/


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## SemiMan (Oct 11, 2014)

He is just another Joe with an opinion. Statististically perhaps a touch of UV but not enough to make photochromic lenses change.


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