HPS will be a heat issue, the CFL's will also create a lot of heat in that small of a space. You can get 4 ft cool white T5 shop lights, I'd recommend four of them one in each corner then get a 150W CFL for the overhead. You can go to dollar tree and pick up reflective window visors for cars for a buck each, they work great for reflecting the light. The light you're using now is not efficient at all. Do you have a window you can set them near for now? My friend once made the exact same set up(years ago) and used the old round 22W flourescents and covered the inside with tin foil, he got about a solid ounce out of a couple of plants.

DO NOT PURCHASE INEXPENSIVE CFL'S, THERE HAVE BEEN MANY REPORTS OF BAD SOLDERING CAUSING THEM TO CATCH FIRE. I suggest GE, at least the article read said they use a better process in assembling them.
Purple Daddy Reviewed by Purple Daddy on . 1st time cardboard growbox ... Need some tips! Hello all, this is my 1st attempt to grow inside a cardboard box and appreciate any pointers you have. Im using one 21 x 18 x 46 wardrobe moving box with a smaller moving box inside to get my seedling close to the light. I also have a second box same dimensions that I was thinking about attaching to expand my grow area for more plants and I also have a small closet that may be used further on down. I needed something quick and cheap because I germinated to early before I had a good setup so I Rating: 5