Beginning in the 17th century, however, as travel on the high seas increased, major coastal lighthouses were constructed to warn mariners of dangerous rocks, reefs, and currents. Twelve lighthouses were constructed in Britain¹s American colonies in the 18th century. The first was built in 1716 in Boston Harbor. By 1900 nearly 1,000 lighthouses, both coastal and harbor types, had been built in the United States. Although estimates vary, as many as 50,000 lighthouses may exist in the world today. At the end of the 20th century, most of these lighthouses were either automated or abandoned. Before the use of electric beacons, the lighthouse keeper had to keep the gas beacon lit, clean the reflecting mirrors, and remove soot from the tower windows. With the introduction of automated electric beacons, the lighthouse keeper became all but obsolete. In addition, modern satellite-based navigational systems that can be installed on ships of all sizes have replaced the lighthouse as a primary navigational aid.
Today, lighthouses that have been automated are used primarily as backups for marine navigation, while many other lighthouses are no longer in operation. Some national governments have turned control of these abandoned structures over to local governments and nonprofit organizations. In many cases, abandoned lighthouses are being turned into parks, museums, inns, and research and educational centers.
The Lighthouse Preservation Society defines “Lighthouse” for the Microsoft Encarta Encyclopedia: