To clear up a few things. Near UV is UV light with short wave lengths. Not long as stated above.
UV-A (aka long-wave UV) ranges from 400 - 320 nm, UV-B from 320 - 280 nm and UV-C from 280 - 200 nm. Technically all of this is 'near UV' with 'far UV' ranging from 200 - 1 nm. As such, what I should have said and what I meant is that blacklights produce UV mostly near the visible spectrum, that is, mostly UV-A which is not particularly dangerous. They produce very little UV-B (damaging) and essentially no UV-C (DEADLY). UV-A is long wavelength UV light, not short...
Being too weak to cause any damage is too broad a statement to make any sense.
I believe I said, "...they probably don't put out enough UV to cause any real harm, though realistically without taking some measurments it's hard to say." I did not say that UV-A cannot be damaging or that UV light in general cannot be damaging, but that a blacklight likely cannot produce enough UV light of any wavelength (especially considering that they produce mostly UV-A, which is not very damaging) to be a serious threat. You'll get more UV-A from the midday sun in 10 minutes than you will in 12 hrs a foot from a blacklight. Considering the very slow rate with which sea water aborbs UV as compared to other wavelengths of light, it is very likely that organisms on reefs get more UV than this even in deeper water (100 ft. +).
Like any type lighting, it depends how many watts you are using. I would not be too afraid of a 2 watt bulb, while a 200 watt bulb may be able to do serious damage fast.
Firstly, is not the discussion about blacklights? Have you every seen a 200 watt blacklight or onenthat focuses its light to the same area as a 2 watt bulb? And for that matter, the wattage the light takes is meaningless: only the amount of UV light matters. For example, I couldn't care less about standing in front of a bank of fluorescent bulbs that take 10,000 watts to run. I wouldn't want to stand in front of even a single 54 watt UV sterilizer bulb though.
Isn't the reason that some corals have such vibrant flourescent colors is to reflect some of the UV rays bulbs put out, so wouldn't that just make them more colorful to counteract the added UV of a blacklight if introduced the light to them slowly and over time?
No. Corals use compounds such as mycrosporine-like amino acids to absorb damaging UV-B. These do not emit fluorescense that we can see so they are, to our eyes, colorless pigments. Green fluorescent protein and all the GFP-like fluorescent and non-fluorescent proteins (all the ones that give corals their nice colors) absorb light in the visible spectrum or slightly into the UV-A. We still aren't sure what the function of these proteins might be (their function might have nothing to do with the fact that they absorb and fluoresce light, or then again it may) but whatever their function they have nothing to do with protecting corals from UV light. They don't absorb UV light that corals need protection from.
Chris