Ingenious use of plastic bottles for a light source in the Philippines. Electricity in the Philippines is the highest of all the Asia nations. While most of the poorer regions do have electricity it is just not cost effective for them to use it for lighting.
Many of the housing have tin roofs and cinder block building construction without many windows, so empty plastic bottles filled with water and a little bleach, to kill any algae, is used in place of electric lighting. The cost of materials to make them is about a dollar and of course an empty bottle.
The project is called “Litre of Light” and they install about 2000 of these a week.
And another video on the same topic.