A lighthouse.

An aid for navigation at sea, a lighthouse is a tower building or framework sending out light from a system of lamps and lenses or, in older times, from a burning fire. More primitive navigational aids were once used such as a fire on top of a hill or cliff, (see beacon). Because of modern navigational aids, the number of active lighthouses has declined to fewer than 1,500 worldwide. Lighthouses are used to mark dangerous coastlines, hazardous shoals away from the coast and safe entries to harbors.

The light is used efficiently:

  • vertically the light is bundled into horizontal directions
  • horizontally the light is bundled into one or a few directions at a time, but sweeping around, so that it can be observed from every horizontal direction

Thus an observer, rather than seeing a continuous weak light, sees a brighter light during short time intervals. These instants of bright light form a pattern specific for the particular lighthouse, e.g. for that of Scheveningen the time intervals between these instants are alternately 2.5 and 7.5 seconds.

Lighthouses have become popular tourist destinations.

In the United States, lighthouses are maintained by the United States Coast Guard. In the United Kingdom, they are looked after by Trinity House.

Perhaps the most famous lighthouse in history is the Lighthouse of Alexandria, built on the island of Pharos in ancient Egypt. The name of the island is still used as the noun for "lighthouse" in some languages, for example French (phare), Italian (faro), Spanish (faro) and Portuguese (farol).

In the beginning of the 20th century Swedish inventor Gustav DahlÚn invented the AGA Lighthouse which made manned lighthouses obsolote. Today there are no manned lighthouses left in existence.

See also: List of lighthouses and lightvessels, lightvessel, Robert Louis Stevenson, Grace Darling, Jean Guichard

External link

Light patterns for lighthouses in the Netherlands