Blackout (wartime)

Blackout (wartime)

A blackout during war, or in preparation for an expected war, is the practice of collectively minimizing outdoor light, including upwardly directed (or reflected) light. This was done in the 20th century to prevent crews of enemy aircraft from being able to navigate to their targets simply by sight, for example during the London Blitz of 1940. In coastal regions, a shore-side blackout of city lights would also help protect ships from being seen in silhouette against the shore and attacked by enemy submarines farther out at sea hidden from view.

Lights can simply be turned off or light can sometimes be minimized by tarring the windows of large public structures. In World War II, a dark blackout curtain was used to keep the light inside. Tarring the windows can mean a semi-permanent blackout status; Grand Central Terminal's World War II blackout paint was not fully removed from its windows until 2009.