Searchlights or spotlights are powerful light sources that use a parabolic reflector to project a beam of light. They almost always include the means for swiveling or changing the direction of the light beam.
Searchlights are primarily used in military defense applications. They are frequently placed in urban areas in order to identify and track bombers in the event of an air attack. Less-common military uses include the use of searchlights to blind attacking forces or flight crews, although the success of these operations has been limited. In consumer applications, searchlights are used to advertise festivals, fairs, and other public events by drawing attention to the event area. While all previously-mentioned applications employ vertical lights, horizontal spotlights are also employed to temporarily illuminate restricted areas, such as prison grounds and other facilities, in order to discourage or track trespassers.
A swivel-mounted searchlight; a searchlight in operation from an operator's perspective.
Image credit: Phoenix | Mid-Atlantic Air Museums