PRF,
I may try a MH conversion bulb but it has so few lumens, only 36,000, that I am not sure how effective it would be. The top and bottom of the "chamber" will be open (Mylar on the sides but I could hold my hand about six inches from the bulb and though I could feel warmth, it was not close to hot. What I really need to do is raid my coffee can of change, use all my PayPal funds and scrape up a few more dollars and get another system but with a MH bulb. That would allow me to run a second group of six plants and compare the production.
The whole idea of this is not just to get a couple of ripe tomatoes! I have five 105 watt CFL bulbs, two 150 watt HPS lamps, five 14 watt LED panels (including one all red and one all blue) and a 54 watt LED, not to mention an assortment of 13 and 23 watt CFL bulbs and shop lights. More than enough to grow a couple of plants! (and trust me, I'm kicking my behind every day for not using a couple of them this winter rather than relying on the GH - I should have known the lack of sunny days in winter would bite me in the butt). Rather, I'm more interested in what light or combo of lights will give me the most pounds of tomatoes over a 120-150 day post-transplant period, with consideration given to initial investment and operating costs.
This year, I want to start harvesting pounds of tomatoes by the middle of December from plants grown upstairs. I figure I have room for at least 50 plants, 70 if I want to use part of another room. At 3 pounds per week per plant, and $1.50 per pound, that would be a nice bit of change. That's a long way from my goal of having 560 plants producing fruit at a time, but it's a step.
Mike