The math formula for light calculations. You can do the math your self and see it's different for each light wattage and bulb type. The only thing that is the same is 0-12" the lumens are the same you start with. From 12" to ? is how fast you loose the lumens and it's different from wattage to wattage.

I=L/D²

Light output divided by the distance squared FYI.
Zandor Reviewed by Zandor on . quick question? How far/close should my400 hps light be to the tops of me plants ? any help welcome thnx. :) Rating: 5