Cheap way to light homes : Liter of light
‘Liter of Light’ is a global open source movement with the aim to provide an ecologically sustainable and free-of-cost source of interior light to rooms in simple dwellings with a thin roof.
The device is simple: it is a transparent 1.5-2l plastic bottle, typically used for carbonated drinks, filled with water plus a little bleach to inhibit algae growth, fitted through the roof of a house. During daytime the water inside the bottle refracts sunlight, delivering about as much light as a 40- to 60-watt bulb to the interior.
Run by: My Shelter Foundation
Read more about the idea and the related campaign here: http://aliteroflight.org/