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The term blackout refers to a cessation of electric activity through electric power transmission systems.

In general during peacetime, a blackout is an unintentional total electrical power outage. It is sometimes contrasted with the term brownout which is a reduction in power, and selected power outages, when demand exceeds supply.

However a blackout can be intentional, for instance collectively minimizing external light (during war), including upwards directed (or reflected) light, to "hide" from enemy aircraft (in the case of an occupied country: the enemy of the occupying force). Additionally, intentional blackouts can be used in coastal regions to prevent city lights from outlining ships (shore-side blackouts). This makes ships hard to be seen by enemy submarines.

See also

Alternate meanings