I have a 4 bulb 4' t5ho (about 200watts) over a 18" x 50" footprint with 4 feet of headroom. I have 12 plants of various bagseed under it right now vegging away in 4" pots. I'm going to keep at least 2 males, nice and tiny in 4 inche pots, for pollen to chuck on some females if they are nice...