How do you light the inside of a windowless room? With a bottle of water, of course! Driven by the outrageous price of electricity in the Philippines, Illac Diaz developed this economical and environmentally-friendly alternative. And in just four months, more than 15,000 bottles have been installed. How does it work? Imagine cutting a hole in the roof. Light enters, but so does the rain. Now plug the hole with a bottle of water. Sure, the bottle allows light in and not the rain, but the sunlight entering the bottle refracts in the water, spreading out into the room below! See these water bottles in action here.