I use the ADJ UV Cannons. Just picked up another pair for this coming halloween week. Love the things, they put out some massive black light. 2 of them covered a rather large dance area that we were going for. Hung them about 20ft in the air to get ridiculous coverage.
Good:
Large area coverage from one point
"Brighter" output than most other fixtures / cost
Lamp costs are the same as cheaper fixtures
Isn't a flourescent tube
Bad:
Heavy (30+ lbs), so a good rig point is needed.
Less versatile (needs more room to fill out, whereas multiple less powerful fixtures can be evenly spaced)
Lamp must be special ordered most of the time, tubes can be found at any hardware store.
takes about 10 minutes to become fully "charged"
Old rumor that was told to me was that these mercury vapor lamps were used to light the white stripes on the runway for airplanes to see at night.