Plastic bottles light up homes for millions

In 2002, a Brazilian mechanic named Alfredo Moser invented a zero-cost daytime lighting technology that does not consume electricity. This technology is very simple but extremely practical, especially for relatively impoverished areas.

Moser utilized the principle of light refraction, which refers to the change in the direction of light as it passes from one medium to another. He embedded plastic bottles filled with distilled water and bleach into rooftops, with part of the bottle exposed on the roof to receive sunlight. When the light passes through the water-filled plastic bottle, its direction changes, scattering in all directions. Over an equal area, the brightness provided by the plastic bottle far exceeds that of a glass window.

The addition of bleach to the water prevents it from turning green over long periods. The brightness of the light depends on the intensity of the sunlight and the clarity of the water. In general, this lighting system is equivalent to a 40-60 watt electric light bulb.