Editing Lighthouse (section)

==Technology==

In a lighthouse, the source of light is called the "lamp" (whether electric or fuelled by oil) and the light is concentrated, if needed, by the "lens" or "optic". Power sources for lighthouses in the 20th–21st centuries vary.

===Power===
Originally lit by open fires and later candles, the [[Argand lamp|Argand hollow wick lamp]] and [[parabolic reflector]] were introduced in the late 18th century.

[[Whale oil]] was also used with wicks as the source of light. [[Kerosene]] became popular in the 1870s and electricity and [[acetylene]] gas derived on-site from [[calcium carbide]] began replacing kerosene around the turn of the 20th century.<ref name="Crompton"/> Carbide was promoted by the [[Dalén light]], which automatically lit the lamp at nightfall and extinguished it at dawn.

In the second half of the 20th century, many remote lighthouses in [[Russia]] (then [[Soviet Union]]) were powered by [[radioisotope thermoelectric generator]]s (RTGs). These had the advantage of providing power day or night and did not need refuelling or maintenance. However, after the collapse of the Soviet government in 1990s, most of the official records on the locations, and condition, of these lighthouses were reportedly lost.<ref>{{Cite web|url=http://www.bellona.org/english_import_area/international/russia/nuke-weapons/nonproliferation/28067|title=Nuclear lighthouses to be replaced - Bellona|date=June 23, 2011|archive-url=https://web.archive.org/web/20110623055427/http://www.bellona.org/english_import_area/international/russia/nuke-weapons/nonproliferation/28067 |archive-date=2011-06-23 }}</ref> Over time, the condition of RTGs in Russia degraded; many of them fell victim to vandalism and scrap metal thieves, who may not have been aware of the dangerous radioactive contents.<ref>{{Cite web|url=http://www.bellona.no/bellona.org/english_import_area/international/russia/navy/northern_fleet/incidents/37598|title=Radioisotope Thermoelectric Generators - Bellona|date=March 15, 2011|archive-url=https://web.archive.org/web/20110315151209/http://www.bellona.no/bellona.org/english_import_area/international/russia/navy/northern_fleet/incidents/37598 |archive-date=2011-03-15 }}</ref>

Energy-efficient LED lights can be powered by [[solar panel]]s, with batteries instead of a Diesel generator for backup.<ref name=baraniuk/>

===Light source===
Many Fresnel lens installations have been replaced by rotating [[aerobeacon]]s, which require less maintenance.

In modern automated lighthouses, the 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 obstruction lights used to warn aircraft of tall structures. Later innovations were "Vega Lights", and experiments with [[light-emitting diode]] (LED) panels.<ref name="Crompton"/>

LED lights, which use less energy and are easier to maintain, had come into widespread use by 2020. In the United Kingdom and Ireland about a third of lighthouses had been converted from filament light sources to use LEDs, and conversion continued with about three per year. The light sources are designed to replicate the colour and character of the traditional light as closely as possible. The change is often not noticed by people in the region, but sometimes a proposed change leads to calls to preserve the traditional light, including in some cases a rotating beam. A typical LED system designed to fit into the traditional 19th century Fresnel lens enclosure was developed by Trinity House and two other lighthouse authorities and costs about [[Euro|€]]20,000, depending on configuration, according to a supplier; it has large fins to dissipate heat. Lifetime of the LED light source is 50,000 to 100,000 hours, compared to about 1,000 hours for a filament source.<ref name="baraniuk">{{Cite web|author=Baraniuk|first=Chris|date=15 September 2020|title=When changing a light bulb is a really big deal|url=https://www.bbc.co.uk/news/business-53756582|url-status=live|website=BBC News|archive-url=https://web.archive.org/web/20230619143546/https://www.bbc.com/news/business-53756582|archive-date=Jun 19, 2023}}</ref>

====Laser light====
[[File:Point Danger lighthouse.jpg|thumb|upright 0.6|[[Point Danger Light|Point Danger lighthouse]], [[Queensland]], 1971]]
Experimental installations of [[laser]] lights, either at high power to provide a "line of light" in the sky or, utilising low power, aimed towards mariners have identified problems of increased complexity in installation and maintenance, and high power requirements. The first practical installation, in 1971 at [[Point Danger Light|Point Danger lighthouse]], [[Queensland]], was replaced by a conventional light after four years, because the beam was too narrow to be seen easily.<ref>{{cite web |title=Point Danger Lighthouse |url=https://lighthouses.org.au/qld/point-danger-lighthouse/ |publisher=Lighthouses of Australia Inc. |access-date=11 August 2020 |language=en-AU |date=26 January 2018}}</ref><ref>{{cite journal |title=Lasers |journal=Aids to Navigation Manual |date=March 2010 |page=43 |publisher=[[International Association of Marine Aids to Navigation and Lighthouse Authorities]] |location=St Germain en Laye, France}}</ref>

====Light characteristics====
{{see also|Light characteristic}}
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 a lighthouse.<ref>{{Cite web |title=Aids To Navigation Abbreviations |url=http://www.uscgboating.org/safety/aton/abbreviations.htm |archive-url=https://web.archive.org/web/20080925160404/http://www.uscgboating.org/safety/aton/abbreviations.htm |archive-date=September 25, 2008}}</ref> For example, the [[Scheveningen Lighthouse]] flashes are alternately 2.5 and 7.5&nbsp;seconds. Some lights have sectors of a particular color (usually formed by colored panes in the lantern) to distinguish safe water areas from dangerous shoals. Modern lighthouses often have unique reflectors or [[Radar beacon|racon transponders]] so the radar signature of the light is also unique.

===Lens===
{{see also|Fresnel lens}}
[[File:Cape Meares Lighthouse lens - Oregon.jpg|thumb|[[Cape Meares Lighthouse]] in Oregon; first-order Fresnel lens]]
Before modern [[strobe light]]s, [[Lens (optics)|lenses]] were used to concentrate the light from a continuous source.  Vertical light rays of the lamp are redirected into a horizontal plane, and horizontally the light is focused into one or a few directions at a time, with the [[light beam]] swept around. As a result, in addition to seeing the side of the light beam, the light is directly visible from greater distances, and with an identifying [[light characteristic]].

This concentration of light is accomplished with a rotating lens assembly. In early lighthouses, the light source was a [[kerosene lamp]] or, earlier, an animal or vegetable oil Argand lamp, and the lenses rotated by a weight driven clockwork assembly wound by lighthouse keepers, sometimes as often as every two hours. The lens assembly sometimes floated in [[mercury (element)|liquid 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.<ref name="Crompton"/>

Efficiently concentrating the light from a large omnidirectional light source requires a very large diameter lens. This would require a very thick and heavy lens if a conventional lens were used.  The [[Fresnel lens]] (pronounced {{IPAc-en|f|r|eɪ|ˈ|n|ɛ|l}}) focused 85% of a lamp's light versus the 20% focused with the parabolic reflectors of the time. Its design enabled construction of lenses of large size and short focal length without the weight and volume of material in conventional lens designs.<ref name=mhp/>

Fresnel lighthouse lenses are ranked by <!-- "order" should be linked somewhere useful -->''order'', a measure of refracting power, 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 shortest. Coastal lighthouses generally use first, second, or third order lenses, while harbor lights and beacons use fourth, fifth, or sixth order lenses.<ref name="nps"/>

Some lighthouses, such as those at [[Cape Race Lighthouse|Cape Race]], Newfoundland, and [[Makapuu Point Light|Makapuu Point]], Hawaii, used a more powerful [[hyperradiant Fresnel lens]] manufactured by the firm of [[Chance Brothers]].