This is actually a very old technique to light windowless places. The cleverness is using a bottle of water for a nearly zero cost implementation. On sailing

This is actually a very old technique to light windowless places. The cleverness is using a bottle of water for a nearly zero cost implementation. On sailing ships, they would install deck prisms to get light belowdecks. You can still buy replicas: http://www.scientificsonline.com/deck-prism.html http://www.scientificsonline.com/deck-prism.html (note that the flat side is on the deck, the pointy side goes down to spread out the light). A more modern implementation: http://www.boatdeckprism.com/ http://www.boatdeckprism.com/