Lighthouse Glossary of Terms
Aerobeacon: A searchlight-type light originally designed for use at airports and adapted for use in a number of lighthouses.
Acetylene: A fuel used which began to be used in lighthouses after 1910. It was the first fuel to eliminate the need for a keeper to carry oil up the tower, since it could be stored on the ground and an automatic sun valve used to turn the light off at daybreak and on again at dusk.
Aid to Navigation: A buoy, beacon, lighthouse, lightship or any other structure or device installed, built or maintained for the purpose of assisting the navigation of vessels.
Alternating Light: A rhythmic light showing light of alternating colors.
Arc of Visibility: The portion of the horizon over which a lighted aid to navigation is visible from seaward.
Argand Lamp: A hollow single-wick oil lamp. The Argand lamp was named after Ami Argand, the Swiss inventor who developed the design.
Astragal: Metal bar (running vertically or diagonally) dividing the lantern room glass into sections.
ATON: An acronym for Aid To Navigation.
Automated: A lighthouse that has been changed to operate without the aid of a keeper. The light is controlled by a remote control, timers or light and fog detectors.
Beacon: A lighted or unlighted fixed aid to navigation.
Bell: A sound signal producing bell tones by means of a hammer actuated by electricity of fixed aids and by sea motion on buoys.
Breakwater: A fixed or floating structure that protects a shore area, harbor, anchorage, or basin by intercepting waves.
Bug Light: Usually a very small tower.
Bull’s-eye Lens: A convex lens used to concentrate (refract) light.
Caisson Style Tower: Lighthouse built on an iron caisson. A caisson was essentially a hollow tube made of heavy rolled-iron plates. The caissons were bolted together on land, transported into place, sunk and filled with sand, gravel, rock or cement. Some referred to them as coffee pot lights or bug lights. After the invention of the internal combustion engine they became known as spark plug lights.
Cast-iron Tower: Usually cylindrical in shape, these lights became popular in the 1840’s. Cast iron was stronger than stone and comparatively light. They could be manufactured miles away in a foundry, and transported to the site for erection.
Catwalk: A narrow elevated walkway, allowing the keeper access to light towers built out in the water.
Characteristic: The audible, visual, or electronic signal displayed by an aid to navigation to assist in the identification of an aid to navigation. Characteristic refers to lights, sound signals, RACONS, radio beacons, and day beacons. This produces the individual flashing pattern of each light, which allows mariners to tell one lighthouse from another.
Chariot: The wheeled carriage at the bottom of a Fresnel lens assembly, which allowed the lens to rotate around a circular iron track atop the lens pedestal.
Clamshell Lens: Rather than being round as most lenses are the Clamshell, or Bivalve, lenses has a flattened shape reminiscent of a clamshell. They usually have two bull's-eyes, one on each side of the lens.
Clockwork Mechanism: The mechanism that turned the light in early lighthouses. They were made up of a series of gears, pulleys and weights, which had to be wound periodically by the keepers.
Commissioned: The action of placing a previously discontinued aid to navigation back in operation.
Composite Group Flashing Light: A group-flashing light in which the flashes combined in successive groups of different numbers of flashes.
Composite Group Occulting Light: A light similar to a group-occulting light except that the successive groups in a period have different numbers of eclipses.
Cottage Style Lighthouse: A lighthouse comprised of a small one story buildig with a light on top that housed the keeper(s).
Crib: A structure, usually of timbers, that was sunk in water through filling with stone, and served as the foundation for a concrete pier built atop it.
Daymark: The daytime identifier of an aid to navigation. The unique color scheme and/or pattern that identifies a specific lighthouse during daylight hours.
Decommissioned: A lighthouse that no longer functions as a navigational aid.
De-staffed: An automated lighthouse without a light-keeper.
Diaphone: A sound signal, which produces sound by means of a slotted piston moved back and forth by compressed air. A “two-tone” diaphone produces two sequential tones with the second tone of lower pitch.
Directional Light: A light illuminating a sector or very narrow angle and intended to mark a direction to be followed.
Eclipse: An interval of darkness between appearances of a light.
Emergency Light: A light of reduced intensity displayed by certain aids to navigation when the main light is extinguished.
Establish: To place an authorized aid to navigation in operation for the first time.
Extinguished: A lighted aid to navigation, which fails to show a light characteristic.
Fixed Light: A light showing continuously and steadily, as opposed to a rhythmic light. A steady, non-flashing beam. (Do not confuse “fixed” as used to differentiate from “floating”)
Flash Tube: An electronically controlled high-intensity discharge lamp with a very brief flash duration.
Flashing Light: A light in which the total duration of light in each period is clearly shorter than the total duration of darkness and in which the flashes of light are all of equal duration. (Commonly used for a single-flashing light, which exhibits only single flashes, which are repeated at regular intervals.)
Focal Plane: The narrow beam of light emitted from a Fresnel lens or modern optic. The distance from the water surface to the center of the beam is known as the height of the focal plane.
Fog Detector: An electronic device used to automatically determine conditions of visibility, which warrant the activation of a sound signal or additional light signals.
Fog Signal: Any type of audible device that could warn mariners from obstacles during period of heavy fog when the light could not be seen. Bells, whistles and horns, either manually or power operated were all used with varying degrees of success.
Fresnel Lens (Fray-nel’): An optic array manufactured using the design principles of Augustin Fresnel, the French physicist who first established the design, and after whom the Fresnel Lens was named. A type of optic consisting of a convex lens and many prisms of glass, which focus and intensify the light through reflection and refraction
Fuel: A material that is burned to produce light (fuels used for lighthouses included wood, lard, whale oil, tallow, kerosene). Today, besides electricity and acetylene gas, solar power is also used.
Gallery: On a lighthouse tower, a platform or walkway or balcony located outside the watch room (main gallery) and/or lantern room (lantern gallery).
Geographic Range: The greatest distance the curvature of the earth permits an object of a given height to be seen from a particular height of eye without regard to luminous intensity or visibility conditions.
Gong: A wave actuated sound signal on buoys, which uses a group of saucer-shaped bells to produce different tones.
GPS: An electronic system for identifying position, GPS is an acronym for Global Positioning System. A GPS receiver triangulates satellite transmissions to calculate position on the Earth.
Group Flashing Light: A flashing light in which a group of flashes is regularly repeated.
Group-Occulting Light: An occulting light in which a group of eclipses, specified in number, is regularly repeated.
Harbor Light: A light to guide ships safely into a harbor. This is usually a small light at the end of a pier.
Horn: A sound signal, which uses electricity or compressed air to vibrate a disc diaphragm.
Incandescent Oil Vapor (IOV) Lamp: A type of lamp in which oil was forced into a vaporizing chamber, and then into a mantle. Similar to the Coleman lamps, used in camping today.
Inner (or rear) Range Light: The light in a pair of range lights that is situated behind the other as viewed from the water.
Interim Light-keeper: A light-keeper who served on a temporary basis, usually between the appointments of full-time light-keepers.
Interrupted Quick Light: A quick flashing light in which the rapid alternations are interrupted at regular intervals by eclipses of long duration.
Isophase Light: A rhythmic light in which all durations of light and darkness are equal. (Formerly called equal interval light.)
Keeper: The person who takes care of the light in the lighthouse. (The Head Keeper is responsible for the operation of the light station.)
Lamp: The lighting apparatus inside a lens.
Lamp and Reflector: A lamp and highly polished mirror used before the invention of the Fresnel lens and in some current electric lights.
Lantern: A glass enclosure at the top of the lighthouse tower, which housed the lighthouse lens.
Lens: Glass optical system used to concentrate the light in a desired direction.
Lewis Lamp: Invented by Winslow Lewis who patented the design in 1810 its primary advantage was that it used less than half the oil of the prior oil lamps. It added a a parabolic reflector behind the lamp and a magnifying lens made from 4-inch-diameter green bottle glass in front of the lamp, a design similar to an Argand lamp.
Light Sector: The arc over which a light is visible, described in degrees true, as observed from seaward towards the light. May be used to define distinctive color difference of two adjoining sectors, or an obscured sector.
Lighthouse: Enclosed tower with an enclosed lantern built by a governing authority as an aid to navigation.
Lighthouse Board: The nine-member board appointed by the US Congress in 1852, established to manage the lighthouses throughout the United States.
Lightship: A ship, usually fitted with a light beacon on a tall mast that served as a lighthouse where it was not practical to build one.
Light Station: A complex containing the lighthouse tower and all of the outbuildings, i.e. the keeper’s living quarters, fuel storage building, boathouse, fog-signaling building, etc.
Light Tower: A tall structure used to elevate a light beacon so that mariners may see it at a distance.
Log: A book for maintaining records, similar to a diary.
Loran: An electronic system for identifying position, LORAN is an acronym for Long Range Radio Navigation. A LORAN receiver measures the difference in the arrival of signals from three or more transmitters to calculate its position.
Modern Optic: Term applied to a broad range of lightweight, weatherproof beacons used in modern devises.
Nautical Mile: A unit of distance used primarily at sea. The nautical mile is defined to be the average distance on the Earth’s surface represented by one minute of latitude. This may seem odd to landlubbers, but it makes good sense at sea, where there are no mile markers but latitude can be measured. A nautical mile equals about 1.1508 statute miles.
Navigation: Determining a path for travel over water.
Nominal Range: The maximum distance a light can be seen in clear weather (meteorological visibility of 10 nautical miles.) Listed for all lighted aids to navigation except range lights, directional lights, and private aids to navigation.
Occulting Light: A light in which the total duration of light in each period is longer than the total duration of darkness and in which the intervals of darkness (occultation’s) are all of equal duration. Occultations are created by partially blocking, or occulting, the light to make it appear to flash. Also called an eclipsing light.
Off Shore Tower: Monitored light stations built on exposed marine sites to replace lightships. Sometimes called Rock Lighthouses.
Off Station: A floating aid to navigation not on its assigned position.
Order: Size of the Fresnel lens, which determines the brightness and distance the light will travel.
Outer (or Front) Range Light: The light in a pair of range lights that is situated in front of the other as viewed from the water. This light was situated at a lower level than the inner range, to allow both lights to be seen, one above the other.
Parabolic Reflector: A bowl-like metal device shaped to the parabolic curve, silver-plated, reflector with a small oil lamp in the center.
Parapet: A walkway with railings, which encircled the lamp room.
Passing Light: A low intensity light which may be mounted on the structure of another light to enable the mariner to keep the latter light in sight when passing out of its beam during transit.
Period: The interval of time between the commencement of two identical successive cycles of the characteristic of the light or sound signal.
Pharologist: One who studies or is interested in lighthouses.
Pier: A structure extending into navigable waters for use as a landing place, or to protect or form a harbor.
Primary Aid To Navigation: An aid to navigation established for the purpose of making landfalls and coastwise passages from headland to headland.
Prism: A transparent piece of glass that refracts or disperses light.
Private Aid to Navigation: A navigation light that is privately owned and maintained. Sometime they are deactivated beacons that have been reactivated for historic purpose.
Quick Light: A light exhibiting very rapid regular alternations of light and darkness, normally 60 flashes per minute. (Formerly called quick flashing light.)
RACON: A radar beacon, which produces a coded response, or radar paint, when triggered by a radar signal.
Range Lights: Two lights associated to form a range, which often, but not necessarily, indicates a channel centerline. The front range light is the lower of the two, and nearer to the mariner using the range. The rear range light is higher and further from the mariner. When the ship is in the proper channel, the lights will be in alignment.
Red Sector: A portion of a light that is colored red so that a mariner sees a red light if he is approaching a dangerous obstacle.
Reflect: Return or throw back, light.
Refract: Bend or slant rays of light.
Revetment: A facing placed on a bank or bluff of stone to protect a slope, embankment, or shore structure against erosion by wave action or currents.
Revolving Light: One that produces a flash or characteristic due to the rotation of the Fresnel lens.
Rhythmic Light: A light showing intermittently with a regular periodicity.
Riprap: A loose arrangement of broken rocks or stone placed to help stem erosion.
Rock Lighthouse: A lighthouse surrounded by the sea.
Screw-pile Towers: Lighthouses built on poles that were “screwed” into the sea floor. They often supported a small wooden building with a tower and light on top.
Sector: The area of the sea covered by a sector light.
Service Room: Where fuel and other supplies were kept.
Shoal: A shallow area, such as a sandbar or rock formation.
Siren: A sound signal, which uses electricity or compressed air to actuate either a disc or a cup-shaped rotor.
Skeleton Tower: Towers consisting of four or more strongly braced legs often enclosing keeper’s quarters or work rooms and with a beacon on top. With their open design they offer little resistance to the wind and waves, and have withstood many storms. They are also used onshore where the land cannot sustain the weight of a masonry tower.
Solar-powered Optic: Many remote lights are powered today by batteries recharged by solar light.
Sound Signal: A device, which transmits sound, intended to provide information to mariners, during periods of restricted visibility and foul weather.
Spark Plug style light: A Caisson tower that looks somewhat like an automobile spark plug.
Spider Lamp: Shallow brass pan containing oil and several solid wicks.
Stag Light: A lighthouse tended to only by men (i.e. no families).
Tender: A vessel used in the servicing of lighthouses and buoys.
Tower: Structure supporting the lantern room of the lighthouse.
Twin Light: A few lights used to consist of two separate lights to distinguish them from nearby lights.
Ventilator: Round ‘ball’ at the top of most lighthouse towers to provide exhaust for heat of the lamp and air circulation within the tower.
Watch Room: A room, usually located immediately beneath the lantern room, outfitted with windows through which a lighthouse keeper could observe water conditions during storm periods.
Whistle: An air or wave actuated sound signal, which produces sound by emitting compressed air through a circumferential slot into a cylindrical bell chamber.
Wick Solid: A solid cord used in spider lamps that draws fuel up to the flame by capillary action.
Wickie: A nickname given to lighthouse keepers, derived from the task of trimming the wick of the lamps.
Courtesy of United States Lighthouse Society