By installing a 1,5 litre, recycled plastic bottle filled with water and a bit of bleach in his roof, Brazilian mechanic Alfredo Moser devised a clever, water-filled ‘light bulb’ that can light a house during the day without the use of electricity. His material invention is catching on and spreading around the globe, illuminating some of the poorest neighbourhoods in the world.

This water filled bottle invention, known also as the ‘Moser Lamp’, works by refracting (or bending) light through different materials. Light itself travels at a speed determined by the material through which is it traveling. Refraction occurs when light changes speed due to travelling through one material to another with a different density. In this case, light moving from air through water and plastic. So when light hits the water filled bottle, it refracts and spreads light throughout the room beneath.

The intensity of light created by the Moser Lamp is measured as being similar to that emitted from a 40 W or 60 W light bulb, depending on the solar conditions outside. A couple capfuls of bleach are added to the water to prevent the growth of algae. Keeping the water itself clean is essential for ensuring the highest possible quality and clarity of water filtered light.

The Moser Lamp is easily installed by a drilling a hole in a roof and then inserting the bottle. The bottle is held in position with a waterproof sealant or glue. A number of local groups involved with the installation of Moser Lamps are experimenting with different glues to find the best solution in terms of both cost and quality. So far, it seems that silicone-based or polyurethane glues work best. A final installation touch, if available, is a plastic tube such as a black film case to cover the bottle’s cap. This is to prevent the original bottle cap from cracking in the sun. When installed correctly, it is estimated the Moser Lamp lasts between 3 and 5 years before requiring replacement.

In countries such as the Philippines, where the cost of electricity is very high and large percentage of the population live below the poverty line, the Moser Lamp is gaining popularity. It is estimated that the lamp is now installed in over 140,000 homes in the Philippines. It has also been installed numerous other countries around the world including India, Bangladesh, Tanzania, Argentina and Fiji. The MyShelter Foundation, based on the Philippines is even training local people to install the bottles so that they can make some income.

Alfredo Moser himself made a modest amount of money installing his lamps in local houses and his local supermarket in Brazil but he has not become wealthy from his invention. Pride in his ecologically and economically efficient invention is his greatest reward. As he tells the BBC, “It’s a divine light. God gave the sun to everyone, and light is for everyone. Whoever wants it saves money. You can’t get an electric shock from it, and it doesn’t cost a penny.”

You can read more about Alfredo Moser: Bottle light inventor proud to be poor on BBC News Magazine.

Or see how to make one yourself here.