Tom: while you are experimenting, you might want to try using 4 florescent tubes per rack (two sets of lamps). The way things are currently set up, I'd expect the plants to grow unevenly. (Notice in the photos how bright some parts of the flat are, and how dark other parts are.) I observe that the wire rack being used isn't really deep or wide
enough to be holding standard sized flats and allow the lamps to be placed where I'd like them, but if there is any way at all that you can test out 4 bulbs per flat, I'd highly recommend it.