i had mine on 24 hours and seemed to work out great, but i've read a lot since and i've heard people say plants always need some dark periods for growth , also that the difference between 24/0 and 18/6 is not that big as far as growing but can save money on electricity so why not turn em off...i think i may do like 20/4 on my next go round, just to be different, haha, but good luck.