Here's an interesting idea: The slow fall of a mass spins a rotor that powers 10 high-output LEDs. A Virginia Tech student made a lamp using this concept which you can read about here:
http://www.newswise.com/articles/view/537851/?sc=swtr
It is about four feet high and apparently operates more of less the same as an hourglass. But they don't say how often you have to tip the thing over.
