The best way to determine how low you can hang your hps light over your plants is to put your hand rigth on top of your tallest plant, palm down and hold it there for 2 minutes. It is important to hold your hand there for a sustained period of time. If your hand is still comfortable you can continue to lower the light as low 12 inches above the tops of your plants as long as the hand test keeps working. You really do not want an hps light any closer. Remember, that once things get going and the canopy of your garden is established that the hps light can only penetrate the canopy approximately 2 feet. hope this helps! Best of luck! Take care, be well and grow on....