A lighthouse is a tower, building, or another type of structure designed to emit light from a system of lamps and lenses and to serve as a navigational aid for maritime pilots at sea or on inland waterways.
Lighthouses mark dangerous coastlines, hazardous shoals, reefs, rocks, and safe entries to harbors; they also assist in aerial navigation. Once widely used, the number of operational lighthouses has declined due to the expense of maintenance and has become uneconomical since the advent of cheaper and often much more effective electronic navigational systems.
Building
While lighthouse buildings differ depending on the location and purpose, they tend to have common components.
A light station comprises the lighthouse tower and all outbuildings, such as the keeper's living quarters, fuel house, boathouse, and fog-signaling building. The Lighthouse itself consists of a tower structure supporting the lantern room where the light operates.
The lantern room is the glassed-in housing at the top of a lighthouse tower containing the lamp and lens. Its glass storm panes are supported by metal Astragal bars running vertically or diagonally. At the top of the lantern room is a stormproof ventilator designed to remove the smoke of the lamps and the heat that builds in the glass enclosure. A lightning rod and grounding system connected to the metal cupola roof provides a safe conduit for any lightning strikes. Immediately beneath the lantern room is usually a Watch Room or Service Room where fuel and other supplies were kept and where the keeper prepared the lanterns for the night and often stood watch. The clockworks (for rotating the lenses) were also located there. On a lighthouse tower, an open platform called the gallery is often located outside the watch room (called the Main Gallery) or Lantern Room (Lantern Gallery). This was mainly used for cleaning the outside of the windows of the Lantern Room.
Lighthouses near to each other that are similar in shape are often painted in a unique pattern so they can easily be recognized during daylight, a marking known as a daymark. The black and white barber pole spiral pattern of Cape Hatteras Lighthouse is one example. Race Rocks Light in western Canada is painted in horizontal black and white bands to stand out against the horizon.
Aligning two fixed points on land provides a navigator with a line of position called a range in North America and a transit in Britain. Ranges can be used to precisely align a vessel within a narrow channel such as a river. With landmarks of a range illuminated with a set of fixed lighthouses, nighttime navigation is possible.
Such paired lighthouses are called range lights in North America and leading lights in the United Kingdom. The closer light is referred to as the beacon or front range; the further light is called the rear range. The rear range light is almost always taller than the front.
When a vessel is on the correct course, the two lights align vertically, but when the observer is out of position, the difference in alignment indicates the direction of travel to correct the course.
There are two types of lighthouses: ones that are located on land, and ones that are offshore. A land lighthouse is simply a lighthouse constructed to aid navigation over land, rather than water. Historically, they were constructed in areas of flatland where the featureless landscape and prevailing weather conditions (e.g. winter fog) might cause travelers to become easily disorientated and lost. In such a landscape a high tower with a bright lantern could be visible for many miles.
One example of such a structure is Dunston Pillar, an 18th-century tower built to help travelers crossing the heathland of mid-Lincolnshire and to lessen the danger to them from highwaymen. Due to general improvements in transport and navigation throughout the 19th century, land lighthouses became almost totally obsolete as aids to travelers in remote places.
Offshore Lighthouses are lighthouses that are not close to land. There can be a number of reasons for these lighthouses to be built. There can be a shoal, reef or submerged island several miles from land.
The current Cordouan Lighthouse was completed in 1611 7 kilometres (4.3 mi) from the shore on a small islet, but was built on a previous lighthouse that can be traced back to 880 and is the oldest surviving lighthouse in France. It is connected to the mainland by a causeway. The oldest surviving oceanic offshore lighthouse is Bell Rock Lighthouse in the North Sea, off the coast of Scotland.