An Innovative and Cheap ‘Solar Bottle Bulb’ Solution Lights Homes in Manila
This is a really neat solution to the problem of dwellings that could really use passive light; it’s not truly an alternative to something like the gravitylight , which is not passive, but for closely-spaced dwellings that don’t have much in the way of window real estate relative to the interior area, and lack (affordable) electricity, it’s just the ticket to light them up during the day.
This is a kind of light pipe (one version of which is a deck prism seen on some boats). I have to think something like this would have been useful for a playhouse when I was a kid. Some more detailed instructions exist, if you are inclined to employ on of these.