"Lights Off" is a short film created by the World Wildlife Fund to promote Earth Hour -- a time when people around the world turn off all of their electrical appliances for an hour. The film has separate light and dark modes, and will play either the light or dark version depending on whether your computer's webcam detects illumination or darkness. There's also a light switch that you can flip to view either version of the film, no matter how well your computer area is lighted.
Link via The Presurfer | Screenshot: The Presurfer