t12 daylight bulbs rock, i have a couple and they keep the height of my plants really low which is cool for LST or FIMming.
My t12's put out like 1600 lumens of blue light spectrum per tube.
good for veg growth.

And the plants won't burn if they touch the tubes, that's always nice.

t12's are big so that's why people suggest t5's, so you can fit more of them into smaller spaces.

My tubes are cool to a touch keeps my temps real low/ I'm currently trying them with a combination of CFL's. The CFL's just toss off so much more heat. Pretty good on the electric bill too.