Mudd, here is my experience. I have a 2 foot, four bulb T5 fixture, I run two bloom and two veg tubes all the time. I have flowered under T5's and it's not a problem. Can you get as large a yield as a 400W HID? No. I wouldn't Veg past 18 inches Max and keep the lamp close to the plant tops. Don't let the plants touch the leaves for very long, you may have heard it won't burn them, it will. Good luck, these T5'S are pretty good little lights.