When I mentioned growing outside, I didn't mean in soil. I meant growing plants in a hydro system outside.
P.S. With a 600 watt HID you can easily cover a 225 (15x15) square foot area. More if the sides had plants in a vertical system. However I would have went with 4, 150 watt
bulbs. That would give a wider footprint (coverage area) like a 20x20 area, and better overall (even) coverage because the light is coming from 4 directions spread out, instead of just one point. It would also be more versatile, in case you decide to grow in different spaces, or smaller areas and don't need a 600 watt light.