In reefkeeping, T5's are the new black. They allow for more light with
a smaller fixture, the bulbs last quite a bit longer than T-8's, are
cheaper to operate than MH, and put out more light than a compact
fluorescent.

That said, the light available is more a product of the reflector
chosen than the bulb. The t-5 allows a smaller reflector that bounces
more light down into the tank.

I have T-5's over my tank and track lighting in my shop. It allows me
to put light exactly where I need it with no shadows (and I got 15
fixtures on Ebay for 10.00 so the price was right)