starting a new grow. space will be 4.5x4.5 thinking about 7-8 plants so will the 400w give me enough light or should I shoot for the 600w? problem i'm running into is all reflectors I find are ok for 600w hps but only support 400w mh. I dont see why if going for 600w hps I would wanna cheap out when switching to the mh cycle. also I dont live in the boondoggles, electricity flow is constant. do I need a balast?
The ballast is what powers your high intensity lights. Do you mean UPS battery backup? Also, I think a 600w would be great for a 4.5 square, especially for 8 plants.
That's over 20 sq feet, way more room than you need for 7-8 plants. If you plan to stick with 7-8 plants then the 400w will do but the 600w would do even better, and you should consider penning in the grow space to a tighter area. If you plan to use the entire 20+ sq feet then you would need at least 1000w.