A simple mixture of water and bleach, in a 2 liter bottle, is illuminating hundreds of homes in poverty. This concoction can produce the same amount of light as a 60-watt incandescent bulb. It is designed to last for at least five years, as the bleach prevents algae from forming. The science behind it is called refraction. When light hits the water, the sudden change of speed makes the light bend and then dispersed from all angles.