I just did some testing with a light meter on T5's, T8's, HPS and MH.
I veg with a 4' four bulb, and two 2' four bulbs T5's.
I flower with a 400w MH and a 600w HPS on a light-mover.
I have some T8's in early retirement. Even after over-amping the bulbs (dual ballast) these bulbs were in the red on my cheap light meter. The plants were healthy, but growth was considerably slower than the plants under the T5's.
The T5's are well into the green on the light meter. The throw is good up to a plant 20" tall, then the lower halves of the plant show signs of not enough light. If you want to veg taller than 20", going with 6 or 8 bulb should be the way to go.
HPS/MH on the light-mover.....there's not a spot in the room that the light meter doesn't get pegged all the way over. Nothing beats the HPS/MH combination. Spread your branches and stake 'em down and you're off to the races.
I've been fucking around with various lighting options (not interested in LED's) and vegging under T5's works great. Low power usage, low heat, and numerous length and number of bulb options makes T5's such a great light.
Flowering on the other hand.......Unless you have a ton of side-lighting with either CFL's or more T5's, either you go with short plants or get used to smoking popcorn buds.....or go with HPS and MH combined.
Note: I am using easycool 6 sealed fixtures vented outside the grow room. Heat is not an issue if you get something like this.
