I spoke recently with a guy who flowered under 8 T5 orange tubes, which is 40 000 lumens, which is sufficient enough for 6 - 10 lowryders, approx one 400w mh lamp if im not mistaken. Just make sure they are T5 which are automatically HO (high output) which most T8's and T12"s arent. I also heard that theyre coming out with T2's, a 10 000 lumen fl tube 2 inches in diameter, with twice the output as the T5's and less than half the space.
I use 5 T5's for my pre veg chamber, allowing just over a foot of growth