I would do 1200w(2 lights) on one breaker and 1200w (other 2 lights) on the other breaker......most breakers have a amp limit of 15 amps but you want to run 80% of that .... My 600w digital quantum runs at 5.36amps i measured it exactly with an amp meter.... so if yours is as effeicent as mine you could run 2 600w's per breaker and you would be pushing it right at its limit really........do you have 3 breakers?? my aprtment as 3 breakers i put my 1000w on one breaker(9amps) and my fans and timers on the other breaker....I still have my 3rd breaker for my kitchen ...I hope you have atleat 3 breakers or you wont be able to cook and grow at the same time with all those lights.....