I expect with a 48" tank you can have 30w tubes the bulbs are around 3ft. I would try and get two double light unit starters and run 4 x 30w this will give you just over 2wpg which is ok for a good deal of plants. Still couldnt grow red leafed plants under that though. Need to pay some attention to the spectrum of the bulbs as well and may be worth doing some reading up on