I have a 400 watt HPS cool tube light that I'm considering using in my 21" deep x 54" wide x 65" high space. I figured out that makes the wattage out to be about 50 watts per square inch. Is that overkill? Also, I've heard that HID has to be a ways from the tops of the plants, and since my space is so small, I'm thinking that I might not be able to use this light there. Would it be best to go with dwarf plants? At first I thought about 4' shop lights, but that might not be powerful enough to give me the yield I'd like. Thanks for any feedback.