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A lighthouse^Wiki is a tower, building or, framework designed to emit light from a system of lamps and lenses or, in older times, from a fire and used as an aid to navigation and to pilots at sea. Lighthouses are used to mark dangerous coastlines, hazardous shoals, safe entries to harbors and can also assist in aerial navigation. Once widely used, the number of operational lighthouses has declined due to replacement by modern electronic navigational aids.

In a lighthouse, the source of light is called the "lamp" (whether electric or fueled by oil) and the magnification of the light is caused by the "lens" or "optic".

Originally lit by open fires and later candles, the Argand hollow wick lamp and parabolic reflector was developed around 1781 in Europe. In the US, whale oil was used with solid wicks as the source of light until the Argand parabolic reflector system was introduced around 1810 by Winslow Lewis.

Colza oil replaced whale oil in the early 1850s, but US farmers' lack of interest in growing this caused the service to switch to lard oil in the mid 1850s. Kerosene started replacing lard oil in the 1870s and the service was finally totally converted by the late 1880s. Electricity and carbide (acetylene gas) started to replace kerosene around the turn of the century.





Prior to modern strobe lights, lenses were used to concentrate the light from a continuous source. Two tasks were involved:

    * vertical light rays of the lamp are redirected into a horizontal plane
    * horizontally the light is focused into one or a few directions at a time, with the light beam sweeping around; as a result, in addition to seeing the side of light beam, there are instants that one can see the light directly from a further distance away.

Fresnel lens

This concentration of light is accomplished with a rotating lens assembly. In classical period lighthouses, the light source was a kerosene lamp, and the lenses were rotated by a weight driven clockwork assembly wound by lighthouse keepers, sometimes as often as every two hours. The lens assembly usually floated in mercury to reduce friction. In more modern lighthouses, electric lights and motor drives were used, generally powered by diesel electric generators. These also supplied electricity for the lighthouse keepers. Efficiently concentrating the light from an omnidirectional light source requires a lens of very large diameter. This would require a very thick and heavy lens if naively implemented. The development of the Fresnel lens (pronounced FREH nel) in 1822 revolutionized lighthouses in the 1800s, focusing 85% of a lamps light versus the 20% focused with the parabolic reflectors of the time. Its design enabled the construction of lenses of large size and short focal length without the weight and volume of material in a lens of conventional design. Although the Fresnel lens was invented in 1822, it wasn’t used in the US until the 1850s due to the parsimonious administrator of the United States Lighthouse Establishment, Stephen Pleasonton. With the creation of the United States Lighthouse Board in 1852, all U. S. lighthouses received Fresnel lenses by 1860.
Fresnel lenses were ranked by Order, with a first order lens being the largest, most powerful and expensive; and a sixth order lens being the smallest. The order is based on the focal length of the lens. A first order lens has the longest focal length, with the sixth being the smallest. Coastal lighthouses generally had first, second or third order lenses, while harbor lights and beacons had fourth, fifth or sixth order lenses.

Some lighthouses, such as those at Cape Race, Newfoundland, and Makapu'u Point, Hawaii, used an even more powerful hyperradiant Fresnel lens manufactured by the firm of Chance Brothers.

In recent decades, many Fresnel lenses have been replaced by rotating aerodrome beacons which require less maintenance. In modern automated lighthouses this system of rotating lenses is often replaced by a high intensity light that emits brief omnidirectional flashes (concentrating the light in time rather than direction). These lights are similar to the obstruction lights used to warn aircraft away from tall structures. More recent innovations are "Vega Lights" and initial experiments with LED panels

In any of these designs an observer, rather than seeing a continuous weak light, sees a brighter light during short time intervals. These instants of bright light are arranged to create a light characteristic or, pattern specific to the particular lighthouse.  For example, for the lighthouse of Scheveningen the time intervals between these instants are alternately 2.5 and 7.5 seconds.

To assist in distinguishing between lighthouses, the time interval of the light or the color pattern of the lens is varied. Sector lights may additionally have a red or green filter on parts of the lantern house to distinguish safe water areas from dangerous shoals.

Modern lighthouses often have unique reflectors or Racon transponders so the radar signature of the light is also unique.


To be effective the lamp needs to be high enough to be seen before the danger is reached by a mariner. The necessary height is calculated by taking the square root of the height of a light in feet and multiplying it by 1.17, yielding the distance to the horizon in nautical miles.[9]

Where dangerous shoals are located far off a flat sandy beach, the prototypical tall masonry coastal lighthouse is constructed to assist the navigator making a landfall after an ocean crossing. Often these are cylindrical to reduce the effect of wind on a tall structure on less stable soil. An example of this style is Cape May Lighthouse. Smaller versions of this design are often used as harbor lights to mark the entrance into a harbor, such as New London Harbor Light.

Where a tall cliff exists, a smaller structure may be placed atop it as the location is already high above the water, such as at Horton Point Light. Sometimes, such a location can actually be too high as along the west coast of the United States. In these cases, the lights are often placed below the top of the cliff to ensure that they can still be seen at the surface during periods of fog.


A Light Station consists of the Lighthouse tower and all of the outbuildings, i.e. the keeper's living quarters, fuelhouse, boathouse, fog-signaling building, etc. The Lighthouse itself consists of a tower structure supporting the lantern room were 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 daytime heat that builds up in such a glass enclosure. A Lightning rod and grounding system is usually connected to the metal Cupola roof to provide 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 watchroom (called the Main Gallery) and/or Lantern Room (Lantern Gallery.) This was mainly used for cleaning the outside of the windows of the Lantern Room.





As lighthouses have become less essential to navigation, many of their historic structures have faced demolition or neglect. In the United States, the Historic Lighthouse Preservation Act of 2000 provides for the transfer of lighthouse structures to local governments and private non-profit groups, while the USCG continues to maintain the actual lamps and lenses. In Canada, the Nova Scotia Lighthouse Preservation Society won heritage status for Sambro Island Lighthouse and has sponsored a bill to change to Canadian federal laws to protect lighthouses.

Many groups have been formed to restore and save lighthouses around the world. They include the World Lighthouse Society and the United States Lighthouse Society. Another international group is the Amateur Radio Lighthouse Society, which sends amateur radio operators to publicize the preservation of remote lighthouses throughout the world.



Visiting and photographing lighthouses are popular hobbies as is collecting ceramic replicas of them. In some locations, lighthouses have become popular travel destinations in themselves and the buildings are maintained as tourist attractions. In the US, National Lighthouse and Lightship Weekend is celebrated on the first weekend of August and International Lighthouse and Lightship Weekend is celebrated on the third weekend. Many lighthouses are open to the public and Amateur Radio Operators often communicate between them on these days.