searchlight

thumb|Auxiliary Territorial Service|ATS officers-in-training crew a 90 cm searchlight in Western Command, 1944

A searchlight (or spotlight) is an apparatus that combines an extremely bright 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. It is usually constructed so that it can be swiveled about. The most common element used in modern searchlights is xenon (Xe). However, rare-earth elements such as lanthanum (La) and cerium (Ce) are used in phosphors to improve light quality in some specialized searchlights.