No... I do anything from 16/8...17/7...18/6...on same grow... I turn it off when I crash.. I have a small place and I like to sleep w/out the lights, and the safety thing...plus I don't really see mush difference and last year I tried both.. but thats me... in veg as long as you stay close to 2/3 light and 1/3 dark you're fine..