im a little confused too. what im not confused about tho..is ur hood can get as close to the plants as possible without "cooking" them. use ur hand as a scale. if its too hot for ur hand, its to hot for ur plant. if u got good air flow through ur hoo, u shood have no problem droppin it closer. i run up to 4, 1000w er's and they stay cool to the touch and the plants will grow up to the glass and then go sideways across it when i reach my 9ft peak on raising the lights. simple terms...closer the better.