I have a loft setup and been successfully growing using a 600w hps in a 1.2x1.2m tent. (1.8m high loft tent)
I am upgrading to a 1.2x2.4m tent (1.8m high loft tent). From my reading a x2 600w HPS will be just about ok in this area. I dont want the high electric and heat issues so cant add two...