I'm using 400w LED, the height all depends on what the temperature is under neath, i put mine that low to achieve the correct germination temperature(88 - 90 F is the best temp to germinate the girl). So in my case it was 12 inches above soil during the germination. When born i raised it another 12 then another 12, then as high as i could go, to the top of my 2m tent, so it was 4 feet high now, but.. you can also lower LEDs down to 21-26 inches and keep that distance through out the grow until you cant raise the led any higher. I'll lower the led when owered when she is in full flowering.