Perhaps you've performed that old camping trick before, where you created a lantern by shining a flashlight into a water-filled bottle. While that may have helped you find your marshmallows in the dark, imagine how much brighter that bottle would have been if it were lit directly by the Sun. Bright enough, it turns out, that it could brilliantly light up the interior of a one-room house. That's the idea behind the Isang Litrong Liwanag (A Liter of Light) project - it's bringing daytime indoor lighting to the homes of the poor in the Philippines, by installing water-filled plastic pop bottles through holes in their roofs.

Isang Litrong Liwanag is run by the Philippines' MyShelter Foundation, which was in turn established by social entrepreneur Illac Diaz. The group was founded to promote social enterprise, appropriate technology and alternative construction in the region.

The Solar Bottle Bulb, as it is called, was originally designed by students from the Massachusetts Institute of Technology (MIT). Its construction and installation is simple. A clear one-liter pop bottle is filled with water, chlorine is added, then the bottle is squeezed part way through a hole in a piece of corrugated tin. A corresponding hole is cut in the tin roof of a house, the tin-and-bottle is secured over the hole so that the bottom of the bottle hangs down through the ceiling/roof, then caulking is applied to prevent rain from getting in.

When sunlight hits the roof and the top of the bottle, its rays are carried down through the water and dispersed into the interior of the home, giving off about as much light as a 55-watt bulb. Given that many of these homes lack windows, they might otherwise be nearly pitch black inside.

Not only does the system produce light during daylight hours, but it is also providing a living for locals who build and install the Solar Bottle Bulbs, and it diverts bottles that might otherwise end up in a landfill. While the bottles don't provide light once the Sun sets, homeowners do at least have the option of performing indoor activities that require illumination during the day, when the light is available. They could also turn to solar-powered lamps such as the Solar Pebble.

Additionally, some homes do have limited electrical lighting, but the Solar Bottle Bulbs allow their owners to save electricity by not using that lighting before dark.

Illac Diaz has stated that he hopes to outfit one million homes with his system by 2012. We wish him luck in his endeavor.

The video below shows the installation process, and the effectiveness of the bulbs.