LED's throw off UV?

[mrsinbad]

LED\'s throw off UV?

I have a couple of doctor friends and I've been thinking it would be cool to spin a few LED flashlights and give it to them as presents to use with their patients when they say, "AHHHHHHH." My concern is that these LED's may throw off UV which may not be a good thing for their patients.

So, do you guys know if the white 5mm LED's or the 1 watt Luxeons High or Low dome throw off UV? Thanks.

 

[TheFire]

Re: LED\'s throw off UV?

They don't. Not at all. Nothing to be worried about.

 

[tylerdurden]

Re: LED\'s throw off UV?

I think there will be some UV emitted. The amount should be small, though. Blue LEDs (which are used in most white LEDs) will emit more UV than red LEDs. LEDs are *not* purely monochromatic, they do emit broadband output.

[previous thread]

 

[CM]

Re: LED\'s throw off UV?

There is a peak at around 440nm which as as close to UV as you can get, so probably nothing to worry about unless you're going to constantly shine it into one's eyes, which is not good with any type of bright light. The peak is from the blued LED emission (white LED's are really blue LED's with phosphor coating)

 

[The_LED_Museum]

Re: LED\'s throw off UV?

White LEDs should emit *very little* UV. The amount of UV they produce is virtually unmeasurable, so I wouldn't worry about them.

 

[The_LED_Museum]

Re: LED\'s throw off UV?

[ QUOTE ]
CM said:
There is a peak at around 440nm which as as close to UV as you can get, ...

[/ QUOTE ]
White LEDs (blue LEDs with a mainly yellow-emitting phosphor) typically emit a spike of radiation at 450-455nm, and a very broad peak from around 580-630nm; with smaller amounts of light at other wavelengths. They're known to be deficient in violet, blue-green, and red. UV emission should be very minor. In normal use, this should be inconsequential. Modern LEDs of any color should not be put directly up to the eye and left to cook there. Although UV hazards are negligible, they may be bright enough to cause damage by other mechanisms.

 

[eluminator]

Re: LED\'s throw off UV?

While we're on the subject of negligible UV, wouldn't incandescent bulbs radiate a bit of UV? And then there's the evil old sun which radiates a considerable amount if it.

 

[The_LED_Museum]

Re: LED\'s throw off UV?

Standard incandescent light bulbs DO emit a small amount of UV; halogen bulbs emit more because they burn hotter.
And the sun emits a good deal of UV because it burns hotter than any incandescent light bulb could.

 

[Steelwolf]

Re: LED\'s throw off UV?

Anyone know how much light should the doctor's light produce? One of the uses of the light, apart from lighting up your throat when you say "Ahhhh", is to shine in to the eyes to see if there is any response from the pupils. Is there like a minimum and maximum brightness for the light?

I too have a few friends for whom I would like to build such lights.

 

[hpcjerry]

Re: LED\'s throw off UV?

What does "burning hotter" have to do with emitting shorter wavelengths? Or is that a reference to color temperature?

 

[TheFire]

Re: LED\'s throw off UV?

Let me correct my original answer: not anything to be worried about, because they don't emit anything more than you'd be exposed to in the normal course of a day. Bottom line is, you're going to get a sunburn outside, not under any LEDs... The damage caused to eyes by most UV radiation is in the (much) shorter wavelengths, and the main danger of longer wavelengths is the lack of reaction to what visually does not appear to be a large amount of light (but is actually dumping a large amount of non-visible energy into your eyes). This is not a problem with visible spectrum LEDs, so you should not have a problem.

 

[Bandgap]

Re: LED\'s throw off UV?

Maybe I am remembering this incorrectly, but didn't someone post something that said the large amount of blue in Luxeon-produced light confused the eye's natural defences?
So the iris doesn't shut down enough to cope with the extra energy in the blue-biased spectrum?

Steve

 

[hank]

Re: LED\'s throw off UV?

UV shades over into blue -- all high energy photons, sufficient to knock an electron off an atom and change a chemical bond. Once you get into the green to red range, the photons aren't energetic enough to make a chemical change.

Search the Cafe topics for "blue light" - I posted a large Google search collection on eye damage. Blue light causes macular degeneration (cumulative over time). Eye doctors' exam lights now filter blue after a couple of patients had eye damage from overlong use of unfiltered bright lights. Not sure what ordinary MDs have. It's a relatively new medical issue as people live longer.

Hotter means closer to blue -- halogen lamps for example put out more UV.

The warnings about blue light deserve to be taken seriously -- the damage is painless and adds up year after year.

 

[PhotonWrangler]

Re: LED\'s throw off UV?

[ QUOTE ]
hank said:
Hotter means closer to blue -- halogen lamps for example put out more UV.



[/ QUOTE ]

And many halogen stage lamps actually come with warnings about sunburn with prolonged exposure.

S'far as longwave UV is concerned, I would think that
an average patient gets much more longwave exposure
from the ordinary fluorescent lamps overhead.

Ever notice how the ivory-colored plastic in
computer and keyboard cases turns yellow over
time? Seems to happen much faster in an office
environment with lots of fluorescents than
at home, where incandescents, with their longer
wavelengths leaning towards yellow-red, predominate.

I'm going to try placing an assortment of
white LEDs, including luxeons, behind some
Woods UV filter glass and compare the amount
of fluorescence occurring from the filtered light.
I'm willing to bet that it'll be minimal compared to
an equivalent amount of fluorescent light, especially
cool-white lamps.