My 400 hps cost about 43 buck's a month at 18 hours a day on.That is a magnetic ballast. The 600 digital ballast cost even less to run a month if you have the ventilation and the height to run the 600 at 24 hours a day. More light slows growth. Not lumens but hours of light recieved per day. You still have to take into consideration what it would cost if you added the fan you would need pumps you would be using.If the lights are on and the fans are running all that is included in what it would cost to run a 400 for 24 hours a day.Gainsville hooked ya up with the formula.

Ga Grown!