When filled with water (with some bleach to keep out the algae) and snugly inserted into custom-cut holes in a roof, plastic bottles refract the sun's rays, scattering about 55 watts of light across a would-be pitch black room. The new lighting source can be rigged up in less than an hour, and it lasts for five years. … Illac Diaz, the social entrepreneur behind the project, told Reuters that the sustainable and inexpensive light source can boost "the standard of living across the board for the bottom 90 percent of this country." Another woman said she hopes to save 23 dollars per month.
The above video illustrates how the method is being used in Haiti.