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A searchlight (or spotlight) is an apparatus that combines an extremely luminous source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a particular direction, usually constructed so that it can be swiveled about.
The Royal Navy used searchlights in 1882 to prevent Egyptian forces from staffing artillery batteries at Alexandria. Later that same year, the French and British forces landed troops under searchlights.
By 1907 the value of searchlights had become widely recognized. One recent use was to assist attacks by torpedo boats by dazzling gun crews on the ships being attacked. Other uses included detecting enemy ships at greater distances, as signaling devices, and to assist landing parties. Searchlights were also used by battleships and other capital vessels to locate attacking torpedo boats and were installed on many coastal artillery batteries for aiding night combat. They saw use in the Russo-Japanese War from 1904–05.
Searchlights were first used in the First World War to create "artificial moonlight" to enhance opportunities for night attacks, a practice which continued in the Second World War. "Artificial moonlight" was invented by the historian and tank warfare theorist, General J. F. C. Fuller. The term "artificial moonlight" was used to distinguish illumination provided by searchlights from that provided by normal moonlight, which was referred to as "movement light" in night-time manoeuvers.
Searchlights were used extensively in defense against nighttime bomber raids during the Second World War. Controlled by sound locators and radars, searchlights could track bombers, indicating targets to anti-aircraft guns and night fighters and dazzling crews.
Searchlights were occasionally used tactically in ground battles. One famous occasion was the Soviets' use of seachlights during the Battle of Berlin in April 1945. 143 searchlights were directed at the German defense force across the Neisse River, with the aim of temporarily blinding them during a Soviet offensive. However, the morning fog diffused the light and silhouetted the attacking Soviet forces, making them clearly visible to the Germans. The Soviets suffered heavy losses as a result and were forced to delay their invasion of the city.
Second World War-era searchlights include models manufactured by General Electric and by the Sperry Company (of gyroscope fame). These were mostly of 60 inch (152.4 cm) diameter with rhodium plated parabolic mirror, reflecting a carbon arc discharge. Peak output was 800,000,000 candela. It was powered by a 15 kW generator and had an effective beam visibility of 28 to 35 miles (45 to 56 km) in clear low humidity.
Today, searchlights are used in advertising, fairs, festivals and other public events. Their use was once common for movie premieres; the waving searchlight beams can still be seen as a design element in the logo of the 20th Century Fox movie studio, the Fox television network, and their corporate parent 21st Century Fox. The world's most powerful searchlight today beams from the top of the pyramid-shaped Luxor Hotel in Las Vegas. The beam concentrates about 13,650,000 lumens from 39 7kW xenon lamps into its beam of about 9,129,000,000 candela. The brightness emanating from the Luxor lamp room is about twice that which emanates from an equal area of the sun's surface (about 95,000,000 cd/ft2 versus 45,000,000 cd/ft2).
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