Don't know about the lighting issue, but here's a story written in 2000 about these bills. It says the bills were gathered from around the country, and that it was glued to the display which lowered the vslue. The author estimated the value at $30k each because of the glue. How wrong was he? Haha.

http://lasvegassun.com/news/2000/jan/20/horseshoe-retires-1-million-display/