LED update
I bought 40 LEDS that are 14000 mcd each, and wired'em up, and turned them on. I have to say that they are disappointingly dim. I think the problem lies in the cone of light; the data sheet says 40-50 degrees, but I think they really mean 10 degrees. In converting from mcd to Lux, the cone of light is important, because mcd is a measure of intensity, lux is a measure of how much light a source puts out. In this case, going from 45 degrees down to 10 degrees is like 20 times less light.

So, I can increase the power to 70mA instead of 20, but that will just double the light. I could put 200 LEDs at 70 mA on the 10-gallon tank to get enough light, but then it costs $300 for the PCB and LEDs and resistors for a 10-gallon tank. The 55-gallon tank would take more like 1000 LEDs.

So, unless there's a brighter, cheaper LED out there, I'm not sure this LED lighting for a fish tank is going to be worthwhile. A regular flourescent hood for the 55-gallon is like $140, which is a lot cheaper.

The RGB LEDs do look cool, though; but not uniform white. It's basically red, blue and green light, changing color over the surface.