[sphelps]

Certainly no expert on lighting but my understanding of UV light is that it relates to spectrum wavelengths. UV-A is in the range of 315-400nm, UV-B in the range of 280-315nm and UV-C in the range of 200-280nm. Ultraviolet light is by definition not visible so a true UV led would not omit visible light however some of the "UV" Leds on the market peak at 380nm so they omit light in both visible and invisible spectrum most of which falls under UV-A so for the purpose of our hobby and application calling these UV leds seems accurate. Any thing above 400nm however is just plain violet despite often referred to as UV.

I'm only aware of LEDs in the upper UV-A range so the damage they can preform from UV radiation is virtually nothing and are completely safe. Lighting like metal halides have much more light found in the UV-A range therefore requiring UV shields to prevent damage. In terms of UV and coral sunscreen, corals found in swallow waters do create there own sunscreen for UV-A and UV-B protection however I wouldn't attempt such things in your aquarium. For many corals this is just a slime coating which in you can actually remove and use for sunscreen if you're ever stranded on a tropical island. I've read some things regarding SPS corals and color pigments but honestly don't know much about it, the article Stricrazy posted looks to very interesting and something I'll certainly look into further if I ever get more involved in SPS again. However my previous experiences have shown there are much more effective ways of reducing zooxanthellae in these corals to better show color pigments and care should be taken when messing around with too much UV light as this may just bleach corals.

Sterilizers use much lower spectrum, typically UV-C as I understand it which would serve no purpose in aquarium lighting. LEDs in this range would certainly be very expensive if even available.

So again I would stick with what I mentioned earlier avoiding anything much lower than 400nm as it does not aid in growth. Using LEDs that peak at 425nm IMO makes the most sense, how many will depend on what other LEDs you're using. When the time comes and you're more interested in coral coloration then you might consider experimenting but there are many other proven methods that will safely increase coloration without changing lighting.