so can u run a 600w hps bulb in a 400w hps system?Most all digital ballasts will run both MH and HPS and some coil HPS also run MH but you should really check the manufacturer. You cannot run a 600w bulb in a 1000w ballast. You can run a 1000w bulb in a 600w ballast (not very efficiently), but the other way around is pretty dangerous.