On Tue, 23 Sep 2003 09:54:09 +0100, you wrote:

>> I'm working on an art project that involves illuminating large quartz
>> crystals with colored LEDs.  We've discovered that UV LEDs produce a
>> most beautiful effect, but we're unsure how to gauge the danger.  The
>> LEDs specs say that peak power is at 405nm, (400-410nm range).  After
>> quite a long time searching the web, I can't find definitive safety
>> info on 405nm light.  Some suggest that it's outside of the dangerous
>> UV-A range (though only barely), other sites warn of damage from all
>> wavelengths less than 500nm.  Does anyone have any ideas or pointers =
to
>> trusted resources.  Better safe than blind!
>
>You don't say how close to the crystals you are putting the LEDs. I =
would
>think that if you can mount the LEDs and crystals in a manner that means
>people cannot look directly at the LEDs then you will be OK. Ideally =
have
>the LED against a face of the crystal, with a suitable mask so that any =
UV
>has to pass through the crystal to reach the viewing public. If you have=
 any
>doubts about this technique check with your local environmental =
monitoring
>department of the council or labour department to see if they have any =
UV
>monitoring equipment available.

Take a look at the laser safety standards for class I laser products - =
these define power levels
regarded as hazardous at various wavelengths, and specify limits in terms=
 of absolute radiated power
and power density.=20
I think that in the case of LEDs, the light is dispersed at a =
sufficiently wide angle that power
levels are insignificant at any sensible distance - the inverse square =
law is your friend here!

EU standard is BSEN60825 - the corresponding (and almost identical) US =
one is 21 CFR part 1040.10-
this is available online :=20
http://www.access.gpo.gov/nara/cfr/waisidx_01/21cfr1040_01.html

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