MANILA, the Philippines - Plastic bottles jut from the roofs in one Manila slum neighborhood, mushrooming across rows and rows of shanty homes. But they aren't just bottles - they bring light.

Using the simplest of technologies to brighten dim and dreary shanties, the bottles, which contain bleach and water, are placed snugly into a purpose-built hole in the roof. They reflect sunlight and spread it through the room beneath.

As a result, the project called "Isang Litrong Liwanag" which means A Liter of Light, helps some of the poorest people in the Philippines save money and live better - in a renewable way.

"If you can make a grassroots revolution wherein each and every person can have an improvement of life with green technology, then that little - if added together - can cumulatively improve ... Filipino living," said Ilac Diaz, the eco-entrepreneur who launched the project.

"So A Liter of Light lights up the house, saves a lot but at the same time improves the standard of living across the board, of the bottom 90 percent of this country."

The idea was influenced by similar endeavors in the Middle East and Brazil, as well as by a project by a group of students at the Massachusetts Institute of Technology.

More than 10,000 of the bottle lights have been installed across metropolitan Manila and the nearby province of Laguna in the last three months through the efforts of low-income communities, local governments and private partners.

"'That's only water?' my neighbors were asking. 'That's only water', I said to them," said Erlinda Densing, a mother of eight whose 20-square-meter home is now illuminated by a bottle light as bright as a lightbulb.

"Basically, the sun's rays are really bright."

The light can be built and installed in less than one hour.

First, a hole is cut in a corrugated iron sheet, and a one-liter plastic bottle that has been filled with water and about four teaspoons of bleach is inserted. A hole is cut in the house's roof, the bottle is put in, and then the iron sheet is fixed to the roof with rivets and sealant.

"Unlike a hole in which the light will travel in a straight line, the water will refract it to go vertical, horizontal, 360 degrees of 55 to 60 watts of clear light, almost ten months of the year," Diaz said.

The bottles emit clear light for about five years, since the bleach inside prevents the buildup of algae in the water.

Lileta Paningbatan, a mother of five, had four of the "bulbs" installed in her home, and two in the small store she runs, in May.

Reuters