The answer to this riddle according to Mike Stephenson, is when it’s a ‘litre of light’.
This amazingly simple technology is bringing light to thousands of otherwise dark homes, where dwellings are built side by side and back to back, without services.
These simple lights involve a clear plastic bottle filled with water and a little bleach (the latter is to keep the water clear). The bottle is fitted into a hole in the roof, so that the top section is outside in the daylight, and the lower part of the bottle protrudes into the room. (Sealant and the lid on the bottle help to keep it secure and weather proof). The refractive properties of water ensures that the light from the sun becomes omni-directional mimicking an electric light bulb and emitting the same amount of light as a 40–60 W incandescent bulb into the room.
Cheap but effective and means that people can live, work and study in previously dark rooms. The bottles can also be fitted with a small solar panel that saves enough daylight to last 10 hours after sunset.
The E-luminate festival (Cambridge) this year brought the ‘litre of light’ workshop to St. Giles Church where the decorated bottles were used to create beautiful installations, effectively spreading the word about the project. Brilliant!