One of the defining challenges of implementing sustainable design to the point of ubiquity is making the technology simple enough to be easily replicable with very little training, few resources, and marginal costs. This solution is a brilliant (squared!) solution to the problem of lighting dark homes.
The process is stunningly simple. 1) Collect discarded 2-litre clear plastic bottles, and clean all labels/glue off of them. 2) Fill them with filtered water and a dose of chlorine bleach (to prevent biological growth) and cap off. 3) Carefully scribe a circle the size of the bottle in a piece of tin, and carefully cut out a hole slightly smaller than than circle. Punch the edges so that you get short teeth to form-fit around the bottles for stability and tightness of fit. 4) Seal the edge between the bottle and the tin really well. 5) Cut a hole to fit the bottle in the tin roof of the home, set the assembly into the hole, and waterproof around the edge of the tin sheet really well. Voila! A daylight bulb for fractional cost that emits a lot of light, transfers very little heat, requires no power, and costs very little in money or time.
Granted, the bottle will deteriorate in time. Light bulbs burn out too, and they have the added challenges of an ongoing operating cost, fragility, and manufacturing complexity.
The idea could easily be translated into more complex and robust forms for integration into first-world architecture. I recently was looking at pictures of a solar tube installation Matt Piner (Pinerworks Architecture) was working on to bring light from a rooftop down two floors to a basement. The amount of light that can be transmitted down a shiny tin tube is surprising. A simple water-filled clear plastic container could be installed at the bottom as the diffuser, and would help to reduce the issue of heat transmission through the tube.
What other inexpensive, low-tech solutions are just a concept away from reducing worldwide energy consumption and improving quality of life? Let me know.