You could ask Catalina Aquarium to build you a 2 bulb T5HO light, using a very wide housiing, so the bulbs are separated by about 9 inches. That would give you low medium light, around 40 micromols, with the light sitting on top of the tank. And, the light over the whole substrate would be pretty uniform.
Or, for high light, you could ask them to build a 4 bulb T5HO light, with the bulbs in two groups of 2 closely spaced bulbs, with the groups about 7-9 inches apart, and get high light, around 60-65 micromols of PAR, also with good uniformity of the light over the whole substrate.
With closely spaced bulbs, any more than 2 bulbs gives very high light, making it difficult to avoid constant battles with algae.
Another interesting option would be http://www.catalinaaquarium.com/stor...oducts_id=1819
with the two outer pairs of bulbs on one power cord, the 3rd from each end on another power cord, and the 2 inner bulbs on a 3rd power cord. This would give you as much flexibility as you could possibly ever need.