IF you have a HPS, definitely use it in flower. On very hot days, just use the T5 if your exhaust is inadequate, or add exhaust.
T5s are perfectly suited to vegging, so keep using it for that stage. Then you can add the HPS later.

If you have at least 3x3 feet of space, you might want to look into a HPS400. Sounds like you are already thinking about graduating to the big guns...
stinkyattic Reviewed by stinkyattic on . 110W T5 vs 150W HPS? although I am satisfied with my T5 setup, I would love to see the results if I switched it with a 150w HPS. Also, I would like to know if there is a difference in heat between my 110W T5 and the 150W HPS. Right now the exhaust is just leaving the box and staying in my closet, which is half open, and my intake is drawing cooler air from outside the closet. I have a 4" Vortex hooked up to a carbon scrubber, and as of now my cab stays ~5 degrees warmer than room temp. thanks in advance :) Rating: 5