Are either one of you serious? First of all 6'x7' is not a small space. That's 42 square feet! That's at least 4 x 400 watters! And good luck finding a 500 watter!
just go for a 1000 watt HPS i have had mine in and out of so many different grow rooms and iv used just about ever light available.. my 1000 always blows em out of the water for some reason!
