This exploits one of the predictions of Einstein's general theory of relativity: that the path of a beam of light (which is a straight line in empty space) is bent inwards by the gravity of a massive object.

ECONOMIST: Cosmology: I spy with my little gravitational lens | The

Walk along a wooded path and the Nao diffuses and dims its beam to give you a more expansive view of the terrain.

WSJ: The Petzl Nao: A Smarter Light | At Play

Many Greyhound buses sweep the road ahead with a radar beam, which warns the driver if there is an obstacle in his path.

ECONOMIST: A safety bet