What does dimout mean?
A dimout is a partial reduction of artificial lighting across a town, city, or region, in which lamps are dimmed, shaded, or screened rather than extinguished altogether. The term is best known from the Second World War, when many coastal communities—especially port cities on both sides of the Atlantic—operated under dimout conditions: enough light remained for docks, railways, and streets to function, but the glow was subdued so that enemy aircraft and submarines could not easily pick out targets. In this respect the dimout sat between ordinary nighttime lighting and the total darkness of a blackout, and the two terms are frequently contrasted in accounts of wartime civil defense. Today "dimout" is largely a historical word, appearing mainly in books, museums, and documentaries about the 1940s, and it retains a distinctly period connotation. For readers of history, it captures a precise and evocative idea: the compromise a society strikes between safety and the need to keep daily life faintly alight.
nounA partial reduction of artificial lighting in a place, especially as a wartime precaution, in which lights are dimmed or shielded rather than switched off entirely. It is generally distinguished from a total blackout.
- A partial reduction or shielding of artificial lighting, especially as a defensive measure during wartime, allowing limited activity to continue under reduced visibility.
"During the war, coastal towns operated under a dimout, keeping shipping lanes faintly lit while hiding them from enemy submarines."
"The authorities imposed a dimout along the eastern seaboard to protect convoys from U-boat attack."
"Streetlamps were painted over and windows curtained as part of the city's dimout regulations."
Regular plural; countable, typically referring to the measure as applied in different places or periods.
"Coastal dimouts were enforced more strictly than those inland."
In World War II, port cities didn't go fully dark—they 'dimmed out' just enough to keep ships moving while leaving enemy submarine crews guessing.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dimout
"Dimout" was formed in English during the twentieth century by combining the adjective "dim"—from Old English "dimm," meaning dark or obscure—with the noun "out," on the model of the earlier word "blackout." It arose specifically in the context of wartime lighting restrictions, when the need to describe partial darkening distinct from a total blackout prompted the new compound. Its closest relatives are the other "-out" compounds of the era, such as "blackout" and later "brownout," all built on the same pattern of naming a lighting condition by combining a descriptor with "out."
How dimout is actually used
"Dimout" is a relatively rare, chiefly historical term associated with World War II civil defense, particularly in coastal areas where complete darkness would have halted essential shipping and industry. It carries a period, documentary flavor and is most often encountered in historical writing about the 1940s. Unlike "blackout," it never broadened into general figurative use for memory failure or loss of communication.
Easily confused with dimout
A blackout extinguishes all lights completely, whereas a dimout only reduces or shields lighting so some visibility remains.
A brownout is a deliberate or forced reduction in electrical power supply causing dimmed lights, while a dimout is a lighting-restriction measure, typically for military defense rather than power shortage.