Inserting a filled water bottle on a corrugated tin roof creates instant light inside the dwelling. This idea is a godsend to those who live in home-made dwellings with no electricity. At least in the daytime they can have bright light to get some work done. It's easy to install and replace, a little bleach insures that the water doesn't get murky with algae. It could be used in Western barns and sheds as well. Perhaps it could be used in a DIY children's fort in the back yard, teaching children quite a bit in the process.
The same principle was used to bring light below deck in sailing vessels. Prisms were inserted on the deck, bringing safe light down below where there were great concerns about using candles or kerosene lamps that might cause a fire. In cities you will sometimes see glass panels in the sidewalk that are providing light to areas down below.