Altering lighting bad for fish?

This is actually in regards to our freshwater tank, but the differences are trivial in this case and I trust the opinions here :) Anyhow, here goes.

Situation: We've converted our downstairs family room in to a movie room with a low lumen (not very bright) projector. We've also been considering moving our little freshwater planted tank down there but the light level from the plant lighting would make the screen harder to see.

Proposed solution: I see these posts all the time about LED lighting, and looking at one of the sites mentioned in an earlier post, http://www.ecoxotic.com it looks like these are very modular, so I'm thinking it might be quite feisable to have a couple of LED's on for during movie viewing and then have all on for any other times.

Concerns: I'm not overly concerned for the plants even if they get a little less than recommended lighting, they are beyond hardy, I could probably start doing water changes with bleach and they'd survive but generally speaking, does transitioning to a lower light level do any harm to fish?

Additional question: That site I mentioned earlier, while awesome, is quite a bit more than I want to pay for a few LED lights. Is there any cheaper perhaps DIY type kits that anyone would recommend? I'm not overly concerned with it being high quality as long as the light spectrum is in the ballpark.

eBay has some plant led grow lights for 75-150. The thing to watch for on led is to make sure you get the right spectrum for your plants. Reef LEDs have almost no red. But from your post sound like you know what you're doing.