Hmmm...Never heard of anyone using blacklights before, but I've settled
on fluorescents for a few reasons...
First, they're cheap. I can hang a compact fluorescent lamp with a
gooseneck type fixture and spring clamp for about $12.00.
Low heat level is another advantage of fluoros. Put 'em up close, REALLY
close, and your plants go nuts!
Stealth is a third advantage. The light from compact fluoros looks close
to that from normal incandescents, but your plants love it. And, it's not as
obvious as the light from HPS.
Safety is another factor that can't be ignored. That big ballast box full
of juice near anything combustible, let alone water, is too much for me to
bear!

If I had the guts, money and drive to build a safe setup, I'd go for HPS,
but I'm amazed at the production I'm getting from a few cheap compact
fluoros (and a little mylar, too).