LEDs in the tread and the sidewalls. At a standstill the lights are well-separated, but get moving and they stream together to form a lighted arc powered by the motion of the wheel itself -- no batteries to change or charge. The folks at Cyglo have had the idea for quite some time now but have newly received patents to protect the idea in the US and UK, meaning they're finally close to production. The cost? Unknown, but surely not cheap. Another pic awaits you below, plus a glimpse into the company's inspiration.