So i guess you saw that episode
I just wish they launched the chair into space, but back to the post.
http://www.fortunecity.com/greenfield/bp/16/student.htm
I just did a google search, and although I am not a "master of electricity", in that example makes sense. It doesn't last forever so its not 100% efficient because some energy is lost to lighting the LED but I guess I can see how its more efficient because it charges the battery with the extra energy it has so its more efficient then normal. I don't know. I was actually thinking of trying to build one of these =P.