Will this be the only source of light or just an addition to try for the shimmer effect?
I finished up my first DIY LED
fixture last Friday using ten 3W LEDs and it puts a very nice shimmer in the tank. I've got about $100 into it, but it's the only source of light for my planted 20H and I probably could have done it cheaper by ordering all the components together instead of going to Radio Shack. I plan to post a thread on it either tonight or tomorrow.
If you have other lighting, a few strategically placed LEDs would work. Low-power LEDs might get washed out, so you'd have to play with it.