Founded in 1904, AGA AB was a Swedish industrial gas company responsible for developing and producing a range of technologies used in maritime navigation around the world. AGA burners became commonplace in lighthouses and buoys. AGA also produced Gustaf Dalén's sun valve, which enabled lights to become semi-automatic, turning off in sunlight and increasing the duration that an unattended light could run independently.


A colourless flammable gas used in lighthouse lamps, produced by adding water to calcium carbide.

Alternating Light

A light that flashes different colours during it’s sequence.


An Aid to Navigation can be any type of device that can help in maritime navigation, but usually refers to Buoys, Lighthouses, Lightships, Daymarks, Fog Signals and various types of radio beacons.


The process of converting lighthouses from manned to automatic operation, usually replacing labour-intensive light sources that required frequent attention with electronic technologies that can be monitored and controlled from afar.

Barbier, Benard, et Turenne

French specialists in lighthouse Technolgies, Barbier, Benard, et Turenne developed Fresnel lenses and other apparatus for lighthouses, clockwork rotation mechanisms, fog horns and buoys, as well as prefabricated lighthouse towers. BBT was founded in 1862. The company's expertise in optics also allowed them to branch-out into developing streetlights, airport floodlights and microscopes. The company was ceased to exist in 1982

Chance Brothers

Chance Brothers was a glassworks based in Smethwick, near Birmingham, founded in 1822. They were one of the largest producers of lighthouse and maritime navigational equipment, which included the production of optics, clockworks, fog signalling apparatus, lighthouse lantern rooms, and even whole lighthouse structures built to prefabricated designs. At their peak Chance Brothers employed 3500 workers.


The Characteristic of a navigational aid can refer to a number of factors but is generally the way it appears or sounds to the mariner, including the pattern or colour of it’s light, the number of times it operates/exhibits a light per each cycle. It can also refer to how many times a fog signal sounds, or how many times a radio beacon reports.

Each navigational aid in an area will have a different characteristic so that they can be told apart at night or during reduced visibility, to help pinpoint a location.

Commissioners of Irish Lights

Established under an Act of the Parliament of Ireland in 1786, the CIL are the general lighthouse authority for the Republic of Ireland and Northern Ireland and are based in Dún Laoghaire.


A device used to compress air, often used to feed air-driven fog signals


A Daymark can be a purpose-built unlit structure such as a cairn or an easily identified tower that can help daytime navigation. The paint scheme on a lighthouse, which can help identify it, is also sometimes referred to as it’s daymark. A daymark’s ‘stripes’ are often referred to as a band of a specific colour.


Derived from a type of organ stop, a diaphone uses a piston that is pushed forward by compressed air or steam to create a vibration. The resonation of the piston creates a low note.

Diaphragm Horn

A type of compressed air horn, similar to those found on railway locomotives or large motor vehicles. These required much smaller and less powerful compressors than earlier Diaphone horns, and replaced explosive fog signals on a number of offshore lighthouses where space was limited.

Electronic Fog Signal

An electronic sound device that can emit a loud high-pitched tone. Electronic fog signals have replaced most other higher maintenance types, such as those that relied on compressed air.

Explosive Jib

A long metal arm that was usually mounted on the roof of a lighthouse, which could be lowered down to the gallery, where an explosive charge was mounted on the end, before being raised to a safe distance above the lantern of the lighthouse, before the charges were detonated. The detonation of these charges at a specific interval could help identify the lighthouse.

Fixed Light

A light that is permanently exhibited, with no flash or period of darkness.

Fog Bell (or Gong)

A fog bell is one of the simplest fog signal devices; it can be wave actuated when mounted on a buoy or sounded by a striking mechanism at regular intervals. Many fog bells have been phased-out in favour of louder alternatives, which can be heard from a larger distance. Gongs are also sometimes used to create a different sound, for identification purposes.

Fog Cannon

A cannon that would be fired at regular intervals to warn of a hazard, usually smaller than a conventional cannon.

Fog Detector

In development in the 1950s and 60s, the earliest fog detectors used a search lamp and a light detector; if enough moisture was present in the air, it would reflect light back to the light sensor and trigger an automatic fog signal to operate. More modern systems use infrared technology. Prior to fog detectors, fog signals were sounded at the discretion of the operator (often lighthouse keepers) based on visibility.

Fog Horn

An audio device used to warn ships of danger

Fresnel Lens

One of the most significant advances in lighthouse technology, the Fresnel Lens was developed by Augustin-Jean Fresnel. These lenses magnify light using an array of glass prisms that surround the light source, which focus light into a central plano-convex lens, like that of a magnifying glass. This makes a light appear much brighter and makes it visible from much further away. The first lens was tested from the unfinished Arc Du Triomphe on August 20th 1820, it's light was witnessed by Louis XVIII and the Commission des Phares from nearly 20 miles away. The lenses were then installed at Cordouan Lighthouse and lit for the first time on July 25th 1823.

Isophase Light

An isophase character is one where the period of darkness is equal to the period of time in which the light is lit. The lamp is ‘off’ and flashes ‘on’ for the same amount of time as it was ‘off’, before repeating the cycle.


Light emitting diode


The enclosure or room in which a lamp or light source is displayed from. The lantern provides protection for the lighting apparatus.

Mercury Bath

A circular trough of mercury that is used to float heavy optics on, so they can be rotated with very little friction, allowing small clockwork or motors to drive them. Due to the toxicity of Mercury, many lighting systems that utilize it are being replaced.

Northern Lighthouse Board

Founded in 1786 as the Commissioners of Northern Light Houses, the NLB are the general lighthouse authority for Scotland and the Isle of Man and are based in Edinburgh.

Occulting Light

An occulting character is one where the period of darkness is shorter than the period of time in which the light is lit. The lamp is ‘on’, and it flashes ‘off’ at set intervals.

Parabolic Reflector

First used at Hunstanton Lighthouse in 1776, a parabolic reflector is essentially a mirrored dish, which when mounted behind a light source can reflect and focus light. The development of oil lamps used in conjunction with these reflectors lead to the replacement of coal-fired lights across the country. Although one of the earlier advancements in lighthouse technology, the parabolic reflector was still in use in UK lightships until automation in the 1980s and 1990s, and at Walney Island lighthouse until 2003.

Paraffin vapour burner

First exhibited by Trinity House from Dungeness Lighthouse on 24th June 1920, the paraffin Vapour Burner (PVB) was widely used in lighthouses, replacing earlier wick lamps. A hand-pump would be used to pressurize the air, which forced liquid fuel from a reservoir into a chamber, from which vapour is burned. The burning vapour heats a mantle, which becomes incandescent. The last PVB in Trinity House service was replaced during electrification at St Mary's lighthouse in 1977.

Receiver Tanks

Large metal tanks that hold large volumes of compressed air to power a fog signal

Sector Light

A coloured light, sometimes completely separate from the main light, but can also be shown as a shaded arc of the main light in which it appears to be another colour to warn of a specific hazard, i,e; a sandbank or rocks. Most often these arcs are Red, Green, or White, and there can be multiple of each.

Service public des phares et Balises

The public service of lighthouses and beacons is responsible for the operation of coastal aids to navigation in France. The service was founded in 1806.


A siren uses a rotor that is spun by compressed air to emit a loud noise, usually amplified and directed by large metal trumpets or horns.

Standby Lamp

A lamp or separate light source to replace the main light source should it or it’s fuel/electrical supply fail.


A brand name of a speaker device used in fog signals, usually installed in large banks, seeing service from the 1960s onwards.

Trinity House

The Corporation of Trinity House of Deptford Strond, more commonly known as Trinity House, is the authority for lighthouses in England, Wales, the Channel Islands and Gibraltar; also responsible for a network of buoys, lightships and satellite/radio navigation systems. The corporation was formed on 20th May 1514 by Royal Charter granted by Henry VIII to license and regulate pilots on the river Thames. Elizabeth I's Seamarks Act enabled Trinity House to "at their wills and pleasures, and at their costs, [to] make, erect, and set up such, and so many beacons, marks, and signs for the sea… whereby the dangers may be avoided and escaped, and ships the better come into their ports without peril".

They constructed their first lighthouse in 1609, at Lowestoft, and established the world’s first lightship in 1732. Throughout the corporation’s history they have led the way in scientific and engineering innovations and technology to aid the mariner.

United States Lighthouse Service

Successor to the United States Lighthouse Establishment (1789), the United States Lighthouse Service was founded in 1910, and operated until 1939 when it was superseded by the United States Coast Guard.

Wick Burner

Like a conventional household oil wick burner, this form of illumination was still used