I used 48" fluorescent tubes for a long time, and always held them to about an inch above the tops of the plants (that is standard procedure with tubes) ... recently, I built a 'starter cabinet' with an 85-watt blue spectrum CFL ('supposedly' 500-watt equiv. :wtf ... what a surprise ... even at 6"-8" distance, my younguns don't stretch, and seem 'shy' of the light ... the CFLs obviously have much more concentrated light, requiring more distance :jointsmile: