Sometimes solutions to problems can be amazingly simple. I sometimes believe that we in the western world are hardwired to look for more complicated methods to solve problems we may have.
The following video will show you an example of something that will leave you saying "why didn't I think of that?".
Many people in developing nations live in dimly lit buildings with corrugated metal roofs. Imagine all the light that can be brought into their lives and all the 2 litre pop (soda for you Yankees) bottles that can be kept out of landfills. I think this simple idea is a winner on many levels.