***Disclaimer: Sphelps, I'm not ripping into you here and I am agreeing with you on the set-up. I just need to say something here because it's the same deal with the debate surrounding red and green LEDs, where people whip out the "science" without considering all the science at play. So... This is more of just a general comment and not actually directed at you because everything you said is entirely true.****
For the record UV LEDs don't stimulate coral growth (Sphelps established that well, good on him), so we need to stop the debate whether they are worthwhile or not in that arena. They are almost entirely aesthetic.
What they do do though is stimulate pigmentation in corals. The pigments act as a "sunscreen" to UV and the pigmentation is what makes them pretty to us. UV also causes fluorescence of certain pigments, which will make certain colors of certain corals appear different or more intense. Green and red LEDs cause the same fluorescence in other pigments, which again rounds out the color visually but add little to the actual growth of the coral compared to the overall usage of white and blue LEDs. White LEDs contain more distinct peaks at various wavelengths compared to the well rounded spectral profile of natural light (and to a lesser extent halide lighting), so some auxiliary LEDs are needed/desired to balance out the colors visually.
Lagoon dwelling corals, especially those that are exposed at low tide, do actually receive significant amounts of UV through out the day, so adding UV LEDs can simulate the amounts they would experience in nature. Now, whether adding this UV actually results in increased coloration in captivity or yields a healthier specimen remains to be seen as this is so new (and I mean real results, not just anecdotal).
Now, the LEDs that are marketed as "UV" in the aquarium hobby aren't UV: they're violet. So all the arguments for the benefits of UV go out the window with these LEDs. Again, they're entirely aesthetic. They are an alternative to the super-blue look of the royal blue where you can get that actinic "pop" without making the rest of your tank look like the Blue Man Group. That said, our eyes are very insensitive to this particular wavelength, so all you would really get is a backlight-like pop of certain colors but only when the main LEDs are off as the effect would be entirely drowned out by the intensity of the rest of the LEDs. So Sphelps suggestion of forgoing the "UV" LEDs and mixing 50/50 425nm and 475nm is awesome. You'll probably be getting more of the effect you are looking for.
AND... Having said all that though, I would also like to whole-heatedly encourage you, Jaws, to not listen to a single word us jaded buggers have said and to go out there and just experiment - you may stumble onto something magic that we're all missing. If you can find a few decent UV-Violet LEDs, give them a go. Based on my knowledge of real UV LEDs (which is far too indepth than I would want to admit), placing them every foot or so might do the job. So in your case that would be a 2x6 grid.
And just as a point of reference, a true 3W UV LED would run you anywhere from $50 to $300 a piece (depending on wavelength) and would barely last 5000 hours of operation. I know this because I just order 7 new ones this morning to replace the ones that just burnt out in 1000 hours on my reactor ( I am finishing a PhD where I am using UV light to split water into pure hydrogen and oxygen to make clean fuels... Like I said, way too indepth knowledge).
Sorry for the rant. Ummm, carry on...
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