UV semi-answers (more info that you really want to know) (disclaimer, this is my understanding)
Fluorescent lights work by when high voltage electrical charge is absorbed by electrons in the atoms of mercury which is in vapor form. These excited electrons do the classical quantum leap and then fall back to ground state---releasing a number of wavelengths of light but largely in the UV range.....hmmmmm. That emitted UV light then encounters the phosphor interior coating that makes the glass tube look white. The process happens again electrons in the atoms of the phosphor coating absorb the UV wavelengths and then emit other wavelengths of lesser energy---visible light. The glass part of the tube filters out the remaining, unabsorbed UV rays. Glass really does a good job of filtering the harmful UV---I've tested this, experimentally, with meters and sensitive strains of yeast. Germicidal lamps are often fluorescents without the phosphor coating and quartz instead of glass. Quartz is transparent to UV.
I doubt that the superbright LEDs used in most flashlights emit any UV. I looked up a couple of emission spectra and I see no evidence of UV emission in common LED's. Here's an example of a tech page with the spectra: http://www.superbrightleds.com/cgi-b...s%2FW18030.htm Notice the the emission bottoms out around 400 nm---which is quite a ways from UV.....There are UV emitting LED's I just doubt they are used in lights.
Can't say much about the little UV curing lights---haven't ever looked into them.
UV is catagorized into 3 "colors" UVA, UVB, and UVC UVC have the shortest wavelengths and this is the light you'll find in germicidal lamps. UVC emitted from the sun typically does not reach the earth's surface but is absorbed in the upper atmosphere. Most of the UVB is as well but some does get to the surface, particularly during high-noon summer. (obviously more at altitude) UVB is typically the causitive agent for skin cancers in that it is absorbed quite readily by DNA molecules in skin cells. UVB has just enough energy to break the normal bonds in the DNA that can then reform to produce an error in that part of the code (over-simplification) That mutation is usually repaired but sometimes not and then when the DNA is copied to make a new skin cell (if it is a reproducing skin cell) the mistake is copied as well. If the mistake/mutation is in a critical region then that cell may have taken the first step to becoming cancerous. Oooppss. I'm rambling on but that gives you a bit of an idea.
UVA has longer wavelengths, less energy and therefore is not generally associated with DNA damage. However, it does have enough energy to damage proteins---like say eye proteins.....hence UV glasses.
Please feel free to look up and verify this info---I'm just doing a brain dump instead of my usual fact checking mostly because I worked quite a while trying to develop relevant student lab investigations in this area.....
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