Looks like you'll need to get some cfls, or a few more of those lights.With cfls, you're gonna need more and more as time goes on and the plants get bigger.
Some of the many varieties of compact fluorescents.
I've never grown with the tube fluorescents,but the cfl's have to get awfully close for better light penetration.The growfaq will explain it to you.
https://www.rollitup.org/view.php?pg=faq&cmd=article&id=587
Or...you could decide to make an investment and buy a HID grow light,which is what most growers prefer.It's gonna cost you a little more initially,but in the long run, it's a much better option.It grows better plants,you don't have to rig up extra fixtures to screw in all those lights because there's just one,it's more like the sun than cfl's,and you won't have a ton of bulbs to recycle.This is a 150 watter.
http://www.htgsupply.com/growlights.asp?categoryID=1&subcategoryID=155&typeID=84 You could grow probably two plants under it, with a couple of extra lights like you have added later on each side of the grow area.With tax and shipping mine came up to almost 90. Or you could get a big one, which requires no additional supplemental lighting.You can grow more plants under it(and even better plants),and it requires no extra lights because it has plenty of power.You will need good ventilation,because it can raise the temps quite a bit.
http://www.htgsupply.com/viewproduct.asp?productID=47981