A liter of light was a project started by the Myshelter Foundation based in the Philippines that provides eco-friendly light through a water bottle and basic physics. The idea behind it is simple: You take a regular plastic water bottle, fill it up with water and chlorine, cut a circular hole on your roof with the same shape as the bottle, and place your bottle (with the cap on) halfway through the hole in the roof. Light coming from the sun will then refract through the water bottle and light up the room below. Alfred Moser, a mechanic in Brazil, originally came up with the idea in 2002 as a way to light up his dark workshop.
The bottle bulbs are currently in 28,000 across the Philippines and are starting to be used in India, Indonesia, and Switzerland. The goal for the project is to install at least 1 million bottles across the world by 2015. For more information about the project, check out their website and video.