I used this light calcuatot on a website and it said the maximum amount of light you need for a 2' by 2' area is like 330 watts of HID light anything more is a waste of power and a 250 works fine in this area. The only reason I say this is because in an area as small as yours, you may have some heat problems, what is your ventilation? also if you do have a slightly bigger area you could get a higher yield from your 400.