Wow! That's huge! I have a very small one that I keep in check by fragging it, as these things grow extremely quickly. In fact, many people try to keep it out of their tanks in the first place, but I really like them as long as they don't spread like crazy, which can be ensured by fragging and placing it in low flow. I'd recommend keeping it in lower flow for that matter, as they spread faster if placed in high flow - they reproduce by growing new branches and letting them go.
Sorry to get off the subject of lighting. I would guess they do best in lower lighting, and I'm honestly not sure if the high lighting will hurt it (I'm sure someone more knowledgeable about this will chime in.)