Athosanswered grow question 6 years ago There are some variables to consider, your ambient temperatures and how well you exhaust heat in the grow space, but somewhere between 2 inches and 12 inches. I use LED lights and keep seedlings 6 inches from the light, fully establish plants on veg up to 4 inches and flowering plants as close as 2 inches. I do it like this to keep the plant as short as possible; but you can use them as far as 12 inches as I said.