Light bulb

A light bulb was a device that used an electrical current to produce light.

If a round metal object were to be placed in between a light bulb and its socket, it would cause a surge and shut off the power. On Venus, Jeff Stone did this with one of his coat buttons while in the Dalek base in the Churchill Mountains, thus allowing their slaves to escape. (PROSE: The Secret of the Mountain) The Seventh Doctor did this with a coin when he and Ace were being held in the Savoy Hotel in an alternate 1951, thus allowing them to escape. (PROSE: Timewyrm: Exodus)

Bernice Summerfield had a joke involving light bulbs and Sontarans: "How many Sontarans does it take to change a light bulb? None, the bulb died a glorious death!" (PROSE: Sleepy)