On 2013-01-15 4:15 AM, William "Chops" Westfield wrote:
>=20
> On Jan 14, 2013, at 10:14 AM, Roger Furer wrote:
>=20
>> They definitely put out UV. I visited a salt water aquarium shop
>> and I commented on the fluorescence of the corals and some fish.
>=20
> Oh come on.  They measure this stuff.  Blue LEDs have a very narrow
> output frequency range, and it doesn't include any "UV."  However,
> blue light is also quite capable of causing some dyes to fluoresce,
> and presumably can cause fading in pigments.  It's not like there's
> some magical property of "UV" (the definition of which is based on
> human vision); you have a more-or-less (quantum exceptions) spectrum
> and the UV is right next to the violet and that's just next to the
> blue.  To cause fluorescence or pigment damage, all you have to have
> is a photon whose energy is sufficient (wavelength small enough) to
> trigger some electron state transition in a molecule somewhere.

It's not that simple. There are various chemical processes in animals
that are sensitive and dependent to various frequencies of light.
Different frequencies cause different chemical/stereo-chemical changes.
Although some of these processes are intentional and have evolved over
millions/billions of years, some are not. We have certainly not yet
discovered the majority of radiation-chemical interactions within
animals (for example, animal cells) but we do know of many harmful
chemical processes that can be triggered at certain frequencies.

And electron excitation is only one of the many ways to change a
molecule. Most of the fun stuff happens on a bit of a "higher level".

> This article implies that the standard excitation frequency for
> various scientific purposes is down around 488nm (Argon ion laser; a
> pretty monochromatic source), which is sort-of blue green.  It also
> has nice explanations of the phenomena in general, and bleaching.=20
> http://www.invitrogen.com/site/us/en/home/References/Molecular-Probes-The=
-Handbook/Introduction-to-Fluorescence-Techniques.html

--=20
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