I found this article online and thought it was pretty interesting...
When you hear the phrase "alternative energy," chances are your mind goes to windmills and solar panels, or perhaps fields of corn. Few people think of human beings as a renewable energy source. But a new lamp design taps into just that idea.
It's not a new concept: Wind-up watches and clocks, and even hourglass-style timekeepers, have relied on humans as energy sources for many centuries. A person winds it up or flips it over, and the device has a renewed supply of potential energy with which to operate. Modern inventions like bicycle-powered blenders and kinetic battery chargers draw on energy stored in the human body, too.
Much like these designs, the gravity-powered lamp envisioned by Clay Moulton, a graduate student at Virginia Tech when his lamp won second place at the 2008 Greener Gadgets Design Competition, relies on people for power. In this case, the people don't wind a gear or pedal a bike; instead, they lift a series of weights back to their starting point. The Gravia lamp is powered by the falling motion of those weights, also known as gravity.
It's an interesting idea, using a (presumably) limitless resource like the pull of gravity to generate power. And while the Gravia lamp requires some advances in technology before it becomes a viable product, the concept is worth checking out.
So what i think is the concept is not only gravity causing the lamp to light, but the potential energy of the masses turning into kinetic energy. Yes gravity is the force behind why that happens, but so far i don't know of anything that can truly be powered by gravity. (Except orbits and such.)