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Lighthouse Glossary.

There are a lot of terms that are used in all aspects of the lighthouse service; some of them are easy to guess but some are not and I have attempted to explain some of the more familiar ones.


Acetylene was a gas used to illuminate lighthouses before town gas and later electricity.

Aldis Lamp is a hand held lamp that could be used to send messages by flashing a light in a frequency similar to Morse Code.

Assistant Keeper is the rank immediately beneath the Principal Keeper.

Beacon is a very visible permanent maritime aid structure. It is not a lighthouse but can be a building or stone structure painted in a striking colour to make it stand out even more. It may or may not carry a light. It can be on land or on water.

Character is the term used to describe the type of light frequency.

Commissioners of Irish Lights is the body controlling all Irish Lighthouses.

Daymark is a very visible permanent maritime aid structure. It is not a lighthouse but can be a building or stone structure painted in a striking colour to make it stand out even more.

Fixed Light is a light showing constantly. When it is switched on then it remains switched on and showing a light until it is switched off. The 'character' would be referred to as a 'Fixed Light'.

Fog Signal is sounded in poor weather conditions; usually when it is foggy. Early light vessels had a fog gong because the sound traveled further. Early lighthouses had a fog bell; some had a fog gun that fired an explosive but later the signal was made from compressed air.

General Lighthouse Authority is a partnership between all three main controlling bodies.

Group Flash is the light character when the flashes are combined in a group.

High Light is one of a pair of lights, the other being the Low Light. See Leading Lights for the definition.

Island Lighthouse is when the lighthouse is built on a small island.

Isophase is the light character when the periods of darkness when the light is not seen equals the periods of lightness when the light can be seen.

Leading Lights is where two lights, when seen from a boat, are in line to indicate a safe passage into the harbour.

Low Light is one of a pair of lights, the other being the High Light. See Leading Lights for the definition.

Lower Lantern is the light normally seen some way below the main light showing through what could be mistaken as a normal window.

Northern Lighthouse Board is the controlling body for Scottish and Isle of Man lighthouses.

Occulting Light is the light character when the flash of light lasts longer than the period of darkness.

Principal Keeper is the most senior keeper of the light.

Rock Lighthouse is one surrounded by sea.

Supernumerary Assistant Keeper is 'supernumerary' - in addition to and not permanent - and referred to a new trainee keeper on probation.

Trinity House is the body controlling all English and Welsh lighthouses.