I have a 135W blackstar LED. I am currently hanging 1 Foot above the plants. Growth seems to be just fine. I know you can put it right on top but The light will have trouble reaching my four plants. Still in early stages of veg. Waiting to knock two out.
Thats a varible question...every LED makers light is pretty different. I keep mine about 16 inches up but I have a 800w 5watt LED Diode model. My Blackstar 240w I keep about 10-12 inches above the plants in that tent.
