I came across a description of a lamp that is powered by gravity recently, called GravityLight. This lamp is powered by raising a weight, and as it is then lowered over a period of 25 minutes it powers a LED light. For people without electricity this is a really low cost way to have light during the night.
Technologies like this have the potential to make a real difference for millions of people. That in itself is worth the effort to come up with solutions like this. Millions of children do not do well at school because they do not have light at night to study. And for many of us the experience of pitch black during the night is unthinkable, because we are surrounded by electricity and lights 24 hours a day.