I had no problem with plant burningg -- kept the light 6+ inches away.

I added 3 cfl (26w ea) under my 436w of T5's. (5.5 x 3 = 16.5 sf)

when I added my first cfl bulb between two plants (I hang them at just below canopy to encourage under-canopy trichome ddev) I was in awe at the changes! I saw leaflets curl and turn away from the light.

I use the lamps with my 12x12, but I can see benefits to running it only 3-4 hours at "mid-day". Lamps will last longer.