Have mine 15-24" from the plants.. notice the stuff closest to the light was going yellow a bit so i backed it down to 3/4ths power and the yellowing slowed but still going a bit. They are also halfway through flower so maybe changing from that but pretty sure its the light. Had a thought to raise it up several inches and turn it up to full power again and see how they handle that. I put the chemdawg under the qb and since then she has gotten her gangster lean on. Fattening up nicely now.