An entrepreneur in the Philippines has come up with an incredible idea for a virtually free 'lightbulb'.
For lots of people in some of the poorest parts of the world, electricity is a luxury they can't afford.
But this simple new idea is bringing new cheap and environmentally-friendly daylight into their lives.
It's called the Litre of Light and it's a plastic bottle filled with water that costs just 50p to make each one.
First, the empty bottle is pushed through a small piece of metal. Then it's filled with water and a little bit of bleach to prevent algae.
When it's fitted into the roof of a building, natural sunlight shining down through the bottle bounces off the water and shines around the inside of the room.