From International Dictionary of Marine Aids to Navigation
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An optical apparatus consisting of a light source and optically refracting or reflecting elements (or both) designed to concentrate light into one or more pencil beams or fan beams (or both), so that, within a limited solid angle, higher values of luminous intensity are produced than by the light source alone.

A projector may be intended to be viewed directly, to illuminate an object to be viewed, or to project an image.

Note: In German a distinction is made between the three functions of projectors mentioned. A projector to be viewed directly is called Signal-Scheinwerfer; a projector to illuminate an object is called Beleuchtungs-Scheinwerfer; a projector to project an image is called Bildwerfer or Projektor.

Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)

International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM