Blackout for more general coverage, or Blackout (World War II).
Talk about it here.
The Black Out was the darkening of London's streets to deny enemy aircraft clear targets, which was implemented early into World War II by the government of Britain, fearing attacks from German bombers. (AUDIO: The Oncoming Storm) Ultimately, the restrictions on car headlamps and street lights at night resulted in more deaths from traffic-related accidents than from air raids. Blackout regulations were relaxed thereafter. (PROSE: Just War)
People were very worried about light being turned on as shown when it was instantly told to people to turn them off. (TV: The Empty Child/The Doctor Dances) Even the Ironsides that Edwin Bracewell "invented" had their luminosity dischargers were covered up. (TV: Victory of the Daleks)