The physics of the concept are straightforward: the bottles are placed in roofs – half outside, half inside – and their lower portions refract light like 60-Watt light bulb but without the need for a power source. A few drops of bleach serve to keep the water clear, clean and germ-free for years to come.
In total, one of these do-it-yourself lights takes maybe an hour to install, cutting an appropriate hole, inserting a bleached-water-filled bottle, and resealing around the resulting gap. Even where clean water is rare, a little can generally be spared for a half-decade of lighting.
We take for granted our electric lights, windows and skylights to access the sun’s glow, but for those living in close-together shacks with corrugated-metal roofs, a stray ray is welcome, and something that can spread light to the darkest interior corners can be a dream come true.
Here is a short clip on how to make it, Use a 2-Liter Bottle as a 50 Watt Light Bulb::