I have 4 Mars Hydro TS1000s in 2 different tents. I run them @ 18" High and at 50% Power during Veg. I then go full blast 100% during flower, staying at 18" above the plants. I believe that is also what Mars recommends. I have had 0 issues with burning of the plants at all. They have gotten as close as 12" for a day or two without issue.