a 600 watt should be enough for 4 plants, but if ya want or think they need more light give to them, you'll get a better yield burning 1200 watts..
i would rotate the plants regular so they all get bit of both..they should stop growing vertical after 2/3 week of 12/12.good luck hope it go's well for ya..
mickrick Reviewed by mickrick on . Is it better to use Metal halide as well as hps lights in flower I an currently 4 weeks into flower, I have four Plants under one 600w hps. They seem to be growing to big and I only have a 600w mh left. Could I use mh as well as hps in flower, would it stop them growing in hight as they are getting a little tall. And what effects would the mh bulb have on the yield and density of the crop. Rating: 5