A lighthouse is a tower, building, or other type of structure
designed to emit light from a system of lamps and lenses and
used as an aid to navigation for maritime pilots at sea or on
inland waterways. Lighthouses mark dangerous coastlines,
hazardous shoals, reefs, safe entries to harbors, and can also
assist in aerial navigation. Once widely used, the number of
operational lighthouses has declined due to the expense of
maintenance and replacement by modern electronic navigational
systems. Lighthouse technology  In a lighthouse, the source of
light is called the "lamp" (whether electric or fueled by oil)
and the concentration of the light is by the "lens" or "optic".
Originally lit by open fires and later candles, the Argand
hollow wick lamp and parabolic reflector were developed around
1781 in Europe and deployed on the Cordouan lighthouse in France
in 1782, with a rotating element being added in 1790. In the
U.S., whale oil was used with wicks as the source of light until
the Argand parabolic reflector sys