I,ve measured my cfl's with a light meter ,8 42 watts on y splitters with diy hood/reflector at 1 '' away the light meter was pinned, for every 1'' you moved it away it would noticeably decrease lummens ,by 6'' it was reading like half the amount of lummens as at 1 '' I increased my yeilds by getting lights closer , just have to be really vigilant in 1st 3 weeks of flower.A fan blowing over tops is a must. I ve had plants grow into the lights,few burned leaves ,no biggie,(i try my best to avoid it) they have to be touching to burn .Stay on top of it and lower your lights ,my last, 1 plant produced 61 g dry .shooting next for 2.5 z's