After reading this post's title, you're probably asking, 'How can this possibly work?' The answer: Plastic bottles filled with water put through holes in a roof, the liquid then refracting the light from the sun, thus filling a room with light.
These faux light bulbs are being fitted to the roofs of home in the slums in Manila, Philippines, and the surrounding region by volunteer programs sanctioned by the government in an effort to bring sustainable energy practices to these poor communities. These are areas where electricity and running water aren't luxuries — they're not even options.
This post on ReNest explains the process: