It's funny at the times I wonder about things like how people use gravity to power grandfather clocks but not really for anything else. Well that is all changing. This group had created a light that works on the same principles as grandfather clocks. They use a weight which harnesses gravity to generate power. Take a look. this is really cool. What a great way to get light in places and times where there is no power to do it any other way!
Brilliant light for developing world is powered by gravity