HPS coverage

I finally figured out how to start a new thread, I am not new to growing. I just thought that I would put it out here to get some feed back, so here are some details: I have a 10'Lx7'Wx8'H I am going to use a 3'x7' area for mother plant and vegging 24/0. that leaves me a 7'Wx7'Lx8'H to flower roughly 20 plants in at 12/12.(all walls are covered in mylar and floor is painted white)I have adequate ventilation and a 8000 btu air conditioner.. So I figure 1 HPS 1000watt light should be sufficient in a 7x7x8 area for flowering 20 plants? If not I have an additional 1000watt HPS? I may have thread whatever its called but all I am asking for is a little feed back, Thanks for understanding!