A distinctive structure, built on or near a shore, which exhibits a light of distinctive characteristics to serve as an aid to navigation. Lesser lights may be displayed from fixed structures called beacons or from floating buoys or lightships. The characteristics of the lights displayed by lighthouses are given in light lists available to mariners and, in abbreviated form, on charts. Some lights have one or more sectors in which the light appears red, usually towarn of some danger in this sector. In other sectors most lights are white.

Lighthouses have been diverse in structure and type of light. Towers up to 200 ft (60 m) were constructed along the Mediterranean coast of Egypt many centuries before Christ, with beacon fires maintained by priests. Logs, coal, oil, gas, and electricity have been used to provide lights. An attendant is continuously on duty at many lighthouses, but some are unattended, and some modern installations are controlled remotely from a convenient location.