A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses and to serve as a beacon for 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 much cheaper, more sophisticated and effective electronic navigational systems.
Before the development of clearly defined ports, mariners were guided by fires built on hilltops. Since elevating the fire would improve the visibility, placing the fire on a platform became a practice that led to the development of the lighthouse.
In antiquity, the lighthouse functioned more as an entrance marker to ports than as a warning signal for reefs and promontories, unlike many modern lighthouses.
The most famous lighthouse structure from antiquity was the Pharos of Alexandria, Egypt, which collapsed following a series of earthquakes between 956 CE and 1323 CE.
The intact Tower of Hercules at A Coruña, Spain gives insight into ancient lighthouse construction; other evidence about lighthouses exists in depictions on coins and mosaics, of which many represent the lighthouse at Ostia. Coins from Alexandria, Ostia, and Laodicea in Syria also exist.
The modern era of lighthouses began at the turn of the 18th century, as the number of lighthouses being constructed increased significantly due to much higher levels of transatlantic commerce. Advances in structural engineering and new and efficient lighting equipment allowed for the creation of larger and more powerful lighthouses, including ones exposed to the sea. The function of lighthouses was gradually changed from indicating ports to the providing of a visible warning against shipping hazards, such as rocks or reefs.
Original Winstanley lighthouse, Eddystone Rock, by Jaaziell Johnston, 1813.
The Eddystone Rocks were a major shipwreck hazard for mariners sailing through the English Channel.The first lighthouse built there was an octagonal wooden structure, anchored by 12 iron stanchions secured in the rock, and was built by Henry Winstanley from 1696 to 1698. His lighthouse was the first tower in the world to have been fully exposed to the open sea.
The civil engineer John Smeaton rebuilt the lighthouse from 1756 to 1759; his tower marked a major step forward in the design of lighthouses and remained in use until 1877. He modeled the shape of his lighthouse on that of an oak tree, using granite blocks. He rediscovered and used “hydraulic lime”, a form of concrete that will set under water used by the Romans, and developed a technique of securing the granite blocks together using dovetail joints and marble dowels.The dovetailing feature served to improve the structural stability, although Smeaton also had to taper the thickness of the tower towards the top, for which he curved the tower inwards on a gentle gradient. This profile had the added advantage of allowing some of the energy of the waves to dissipate on impact with the walls. His lighthouse was the prototype for the modern lighthouse and influenced all subsequent engineers.
John Smeaton’s rebuilt version of the Eddystone Lighthouse, 1759. This represented a great step forward in lighthouse design.
One such influence was Robert Stevenson, himself a seminal figure in the development of lighthouse design and construction. His greatest achievement was the construction of the Bell Rock Lighthouse in 1810, one of the most impressive feats of engineering of the age.This structure was based upon Smeaton’s design, but with several improved features, such as the incorporation of rotating lights, alternating between red and white.Stevenson worked for the Northern Lighthouse Board for nearly fifty years during which time he designed and oversaw the construction and later improvement of numerous lighthouses. He innovated in the choice of light sources, mountings, reflector design, the use of Fresnel lenses, and in rotation and shuttering systems providing lighthouses with individual signatures allowing them to be identified by seafarers. He also invented the movable jib and the balance-crane as a necessary part for lighthouse construction.
Marjaniemi Lighthouse, the 19th-century lighthouse in the Hailuoto island, neighbouring municipality of Oulu, Finland
Alexander Mitchell designed the first screw-pile lighthouse – his lighthouse was built on piles that were screwed into the sandy or muddy seabed. Construction of his design began in 1838 at the mouth of the Thames and was known as the Maplin Sands lighthouse, and first lit in 1841.Although its construction began later, the Wyre Light in Fleetwood, Lancashire, was the first to be lit (in 1840).
The introduction of electrification and automatic lamp changers began to make lighthouse keepers obsolete. For many years, lighthouses still had keepers, partly because lighthouse keepers could serve as a rescue service if necessary. Improvements in maritime navigation and safety such as satellite navigation systems such as GPS led to the phasing out of non-automated lighthouses across the world. In Canada, this trend has been stopped and there are still 50 staffed light stations, with 27 on the west coast alone.
Remaining modern lighthouses are usually illuminated by a single stationary flashing light powered by solar-charged batteries mounted on a steel skeleton tower.Where the power requirement is too great for solar power, cycle charging by diesel generator is used: to save fuel and to increase periods between maintenance the light is battery powered, with the generator only coming into use when the battery has to be charged.
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.
Originally lit by open fires and later candles, the 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 carbide (acetylene gas) began replacing kerosene around the turn of the 20th century.
Carbide was promoted by the Dalén light which automatically lit the lamp at nightfall and extinguished it at dawn.
During the Cold War, many remote Soviet lighthouses were powered by radioisotope thermoelectric generators (RTGs).
These had the advantage of providing power day or night and did not need refuelling or maintenance. However, after the breakdown of the Soviet Union, there are no official records of the locations or condition of all of these lighthouses.
As time passes, their condition is degrading; many have fallen victim to vandalism and scrap metal thieves, who may not be aware of the dangerous radioactive contents.
Energy-efficient LED lights can be powered by solar panels, with batteries instead of a diesel generator for backup.