Alfredo Moser's invention is lighting up the world. In 2002, the Brazilian mechanic had a light-bulb moment and came up with a way of illuminating his house during the day without electricity - using nothing more than plastic bottles filled with water and a tiny bit of bleach. In the last two years his innovation has spread throughout the world. It is expected to be in one million homes by early next year. So how does it work? Simple refraction of sunlight, explains Moser, as he fills an empty two-litre plastic bottle. Add two capfuls of bleach to protect the water so it doesn't turn green [with algae]. The cleaner the bottle, the better," he adds. Wrapping his face in a cloth he makes a hole in a roof tile with a drill. Then, from the bottom upwards, he pushes the bottle into the newly-made hole. "An engineer came and measured the light," he says. "It depends on how strong the sun is but it's more or less 40 to 60 watts," he says. The inspiration for the "Moser lamp" came to him during one of the country's frequent electricity blackouts in 2002. "The only places that had energy were the factories - not people's houses," he says, talking about the city where he lives, Uberaba, in southern Brazil. "It's a divine light. God gave the sun to everyone, and light is for everyone. You can't get an electric shock from it, and it doesn't cost a penny." Moser has installed the bottle lamps in neighbours' houses and the local supermarket. While he does earn a few dollars installing them, it's obvious from his simple house and his 1974 car that his invention hasn't made him wealthy. What it has given him is a great sense of pride.