How to make a light bulb with a plastic bottle and bleach

Thursday, September 27, 2012 16:52
Posted in category Solar Installer Articles

If you look around the neighborhood in Sao Paulo, Brazil from above, you may find a very interesting sight. Bottle tops poking out in the ceiling around the entire neighborhood. What are those bottles for?

In 2002, during an energy crisis and blackout, Alfredo Moser, an engineer in Brazil, discovered that he could escape from working in the dark by hanging water-filled bottles in the roof of his workshop. “On average, the bottles produce as much light as a 50 Watt incandescent bulb,” Electric Engineer Clivenor de Araujo Filho, says after he measured every bottle’s light intensity.

A solar bottle lamb is made by a 2-liter soda bottle with clean water, two lid-fulls of bleach and a camera film dispenser to protect the lid from the sun. 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.

Usually it takes about an hour to install one of these do-it-yourself lights; 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.

Alfredo’s ingenious idea has spread throughout his neighborhood. Many of the solar bottle lambs are installed in Brazil’s “Chico Mendez” park, where it has turned into a mini-attraction. For residents, this invention has helped them save electricity bills. “It’s great, the bathroom used to be very dark. Look how much light there is now, and it is a lot more natural.” Without any windows and a higher electricity bill than her salary, Lidia Araponga got several lights installed.

Though these plastic bottle lamps can works only during the day, they haven’t shown any other disadvantages. In Engineer Jose Marcos de Castro’s workshop, the lights have been there for two years without any maintenance at all. His electricity bill also has lowered since he got them.” It has no problems. When I get here in the morning, they turned on automatically, and at midnight, they turned themselves off.” Also, they never leaks when it rains.

For those living in close-together shacks with corrugated-metal roofs, this invention is especially important. The bottle lamp can spread light to the darkest interior corners during the day. Now this simple design idea has been adopted by MIT students and expanded to other developing areas where many low-income homes lack access to either daylight or electricity.


  • Daniel Watkins

    Um, so what happens when the plastic bottle wears out? I know it’s not biodegradable but intense heat for instance can cause the bottle to shrink and then you’ll have a leak in your roof.