Turning a 2l soda-bottle into a "lightbulb"

Brazilian favela-dwellers without reliable electricity have an alternative means of supplying light to enclosed spaces that have no/insufficient windows (either because they are abutted on all sides by other buildings, or because the walls are made of materials that make it impractical to add windows). They suspend 2l soda bottles filled with a water/bleach solution from the ceiling, with the open tops poking out into the daylight. Sunlight refracts off the water in the bottle and turns it into a "lightbulb" that has been measured as supplying illumination comparable to a 50w incandescent bulb.

(Thanks, Phil!)