A tower or other building with a powerful light at top, erected at the entrance of a port, or at some important point on a coast, to serve as a guide to mariners at night; a pharos.
Structure carrying a powerful light to warn ships or airplanes that they are approaching a place (usually land) dangerous or important to navigation. The light is magnified and directed out to the horizon or up to the zenith by a series of mirrors or prisms. Increasingly lighthouses are powered by electricity and automated rather than staffed; the more recent models also emit radio signals. Only a minority of the remaining staffed lighthouses still use dissolved acetylene gas as a source of power.
Lights may be either flashing (the dark period exceeding the light) or rotating (the dark period being equal or less); fixed lights are liable to cause confusion. The pattern of lighting is individually varied so that ships or aircraft can identify the lighthouse. Among early lighthouses were the Pharos of Alexandria (about 280 BC) and those built by the Romans at Ostia, Ravenna, Boulogne, and Dover. In England beacons burning in church towers served as lighthouses until the 17th century, and in the earliest lighthouses, such as the Eddystone, first built 1698, open fires or candles were used. Where reefs or sandbanks made erection of a lighthouse impossible, lightships were often installed; increasingly these are being replaced by fixed, small, automated lighthouses. Where it is impossible to install a fixed structure, unattended lightbuoys equipped for up to a year's service may be used. In the UK, these are gradually being converted from acetylene gas in cylinders to solar power. In fog, sound signals are
made (horns, sirens, explosives), and in the case of lightbuoys, fog bells and whistles are operated by the movement of the waves. In the US the supervisory authority is the Coast Guard. + prikaži više