Awesome info guys.I have cool tubes and the lights are about 15-18 inches away.I have kept them close the entire way. Strains that have gotten big are: creamatic, royal dwarf, ak auto ,Berry ryder ( some pushing 50 ")Critical auto.There is no way i can raise the lights any more without building a second floor! LOL Several i have just bend branches.My main problem is over crowding.I will consider cutting my numbers down next time around.Somtimes less is more!I thought if i increased light to penatrate canopy i could crowd them alittle. 4x9=36 sq ft - 1800 watts/ 36 = 50 watt per square foot. Which feel is quite sufficient.Also while i have you experienced guys around What cfm fan do feel is proper for venting 3-600 watt hps and still have enough push to get heat through a decent carbon filter. I need to improve from the 220cfm i have now i believe to keep heating issues down.