I am growing five plants in a 5 x 5 tent under HID. I had read that a 600 W bulb was sufficient. However I am also reading Ed Rosenthal's book and he states that a 1000 W bulb is sufficient for a 4 by 4. My seeds are just emerging from their shells. Can I continue with the smaller bulb (saving money on electric bill) until the plants are bigger before switching to the larger bulb or should I switch now? Thank for your help.