How do searchlights work?

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Searchlights or spotlights create a powerful beam of light that can be directed at specific objects or areas.

The rays of light from an electric source are scattered in all directions. This is why a light bulb will light a whole room rather than only some areas. A searchlight uses a mirror to direct those rays in parallel lines.

Mirrors can be plane (flat), convex (curved outwards) or concave (curved inwards). Plane mirrors will reflect the light rays back at 90 degrees or right angles as they hit the mirror, and any light hitting the mirror in a straight line to the mirror’s center will be reflected back in a straight line. Convex mirrors will reflect the light rays back at a greater angle with more scattering or spreading out. Convex mirrors reflect the light rays at a smaller angle in a more inward direction.

Mirrors have what is called a center line and a focus. The center line is an imaginary line drawn through the exact center of the mirror, perpendicular to it. The focus is on this center line, and its distance from the mirror varies depending on the concavity (how curved it is). The focus can be found by directing a light ray straight at the mirror and noting where the light ray that is reflected back crosses the center line. In the opposite fashion, if a light source is placed in the focus of a concave mirror, the light rays that hit the mirror are reflected back in parallel lines, i.e., in a beam. Searchlights make use of this physical property of concave mirrors. Searchlights contain a large concave mirror and have a powerful light source placed at the focus of the mirror. The light from this light source is reflected back from the concave mirror in a powerful beam. Other common items using this property are flashlights (less powerful searchlights) or headlights on a car.

General Electric built the first searchlight, which had 6,000,000 candlepower. It was displayed at the World’s Columbian Exposition of 1893 (the World’s Fair) in Chicago.

In the late 19th century, naval vessels utilized searchlights to find enemy torpedo boats at nighttime. In 1892, searchlights were used for defense along the English Channel. By World War I, searchlights were used to create artificial illumination to facilitate nighttime attacks. During World War II, searchlights were employed to identify the presence of enemy airplanes, with the position of aircraft conveyed from listening posts and, later in the war, from radar stations, to searchlight operators. Pairs of searchlights were also spaced at a known distance apart to determine the altitude of enemy aircraft. Searchlights were also occasionally used in ground battles to blind enemy troops. For example, in the Battle of Berlin in April 1945, Soviet troops directed 143 searchlights at the German forces, but the initiative backfired as, owing to the morning fog, the light silhouetted the Soviet troops, making them visible to the Germans.

Aside from their use by the military, searchlights have been widely employed for security purposes, such as in prisons and security complexes. The focused beams of light can help identify nighttime intruders or escapees. Searchlights are also widely used by law enforcement and rescue vehicles – on land, sea or air – to track missing people, those in need of assistance and criminals.

In the entertainment industry, searchlights are commonly used to focus light on performers on a stage and are often a feature at fairs or public events to light up displays, streets, buildings or the sky. They were once commonly used at movie premieres; the 20th Century Fox movie studio logo still demonstrates the use of searchlights.

Resource by Will

I am the editor for TheFreeResource.com, and owner of LinchpinSEO, a small business content creation company. The Free Resource has a select community of talented writers, teachers, and business people (and we are always looking for more) that bring you the most trusted resources on the web and credible articles about many topics.

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