i tried it just about exactly a year ago when i bought my first coral. lemme tell ya, if u have fish in ur tank be prepared for the frantic spaz swim that will ensue. my fish went NUTS! i read up a bit more on black lights and it turns out that it blinds fish so i personally would not recommend installing one. they may look kool for a little while but my corals didnt really appreciate it either and they showed me this by closing up for 3 days afterwards!

hope it helps, steve