An
aid for navigation and pilotage 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 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 operational lighthouses
has declined to less than 1,500 worldwide.
Lighthouses are used to mark dangerous
coastlines, hazardous shoals away
from the coast, and safe entries to
harbors.
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