My friend is being hounded by a patent troll. He builds these really impressive ball machines out of K'nex. As part of his design, he's fixed LEDs inside of the clear plastic balls so that the structure lights up as the balls roll along their path. He isn't trying to sell the design, but he's made several popular youtube videos based off of the concept. Here's a long exposure pic he made: http://i.imgur.com/76ZGv.jpg

The patent troll claims that he's violating this patent for a "Lighted moving ball display system": http://www.google.com/patents/US8348466

I'm not asking for legal advise. I'm just wondering what constitutes a violation of a patent. How similar do two ideas need to be, what criteria need to be satisfied, and who decides?