Glossary of Lighthouse Terms

The information on Glossary of Terms was obtained from the United States Lighthouse Society.

AEROBEACON:  A modern day type of light presently used in many lighthouses to produce a characteristic.

AID TO NAVIGATION:  Any device external to a vessel or aircraft specifically intended to assist navigators in determining their position or safe course, or to warn them of dangers or obstructions to navigation.

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 wick oil lamp (see wick).

ASTRAGAL: Metal bar (running vertically or diagonally) dividing the lantern room glass into sections.

BEACON: A lighted or unlighted fixed aid to navigation attached directly to the earth’s surface. (Lights and day beacons both constitute beacons).

BELL: A sound signal producing bell tones by means of a hammer actuated by electricity on fixed aids and by sea motion on buoys.

BULLSEYE: A convex lens used to concentrate (refract) light.

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. The individual flashing pattern of each light.

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.

DAYMARK: The daytime identifier of an aid to navigation. The unique color scheme and/or pattern that identifies a specific lighthouse during daylight hours.

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: A relatively brief appearance of a light, in comparison with the longest interval of darkness in the same characteristic.

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.)

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: A device (such as a whistle, bell, canon, horn, siren, etc.) which provides a specific loud noise as an aid to navigation in dense fog. (See sound signal.)

FRESNEL LENS: 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.

GROUP FLASHING LIGHT: A flashing light in which a group of flashes, specified in number, is regularly repeated.

GROUP-OCCULTING LIGHT: An occulting light in which a group of eclipses, specified in number, is regularly repeated.

HOLLOW: A concentric cotton wick used in Argand and other lamps.

HORN: A sound signal which uses electricity or compressed air to vibrate a disc diaphragm.

INOPERATIVE: Sound signal or electronic aid to navigation out of service due to a malfunction.

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.

LANTERN ROOM: Glassed-in housing at the top of a lighthouse tower containing the lamp and lens.

LENS: A curved piece of glass for bringing together or spreading rays of light passing through it.

LIGHT: The signal emitted by a lighted aid to navigation. The illuminating apparatus used to emit the light signal. A lighted aid to navigation on a fixed structure.

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.

LIGHT STATION: A complex containing the lighthouse tower and all of the outbuildings, i.e. the keeper’s living quarters, fuel house, boathouse, fog-signaling building, etc.

LIGHTHOUSE: A lighted beacon of major importance.

LOG: A book for maintaining records, similar to a diary.

NAVIGATION: 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 clearly longer than the total duration of darkness and in which the intervals of darkness (occultation's) are all of equal duration. (Commonly used for single-occulting light which exhibits only single occultation's which are repeated at regular intervals.)

OFF SHORE TOWER: Monitored light stations built on exposed marine sites to replace lightships.

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.

PARABOLIC: A bowl-like metal device, silver plated, reflector with a small oil lamp in the center.

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 tow identical successive cycles of the characteristic of the light or sound signal.

PHAROLOGIST: One who studies or is interested in lighthouses.

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.

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.

REBUILT: A fixed aid to navigation, previously destroyed, which has been restored as an aid to navigation.

REFLECT: Bend or throw back light.

REFRACT: Bend or slant rays of light.

RELIGHTED: An extinguished aid to navigation returned to its advertised light characteristics.

REPLACED: An aid to navigation previously off station, adrift, or missing, restored by another aid to navigation of the same type and characteristics.

REPLACED (TEMPORARILY): An aid to navigation previously off station, adrift, or missing, restored by another aid to navigation of different type and/or characteristic.

REVOLVING LIGHT: One that produces a flash or characteristic.

RHYTHMIC LIGHT: A light showing intermittently with a regular periodicity.

SECTOR: See light sector.

SERVICE ROOM: Where fuel and other supplies were kept.

SIREN: A sound signal which uses electricity or compressed air to actuate either a disc or a cup-shaped rotor.

SOUND SIGNAL: A device which transmits sound, intended to provide information to mariners, during periods of restricted visibility and foul weather.

SPIDER LAMP: Shallow brass pan containing oil and several solid wicks.

STAG LIGHT: A lighthouse with no family living in it, i.e. inhabited by men only.

TOWER: Structure supporting the lantern room of the lighthouse.

WATCHING PROPERLY: An aid to navigation on its assigned position exhibiting the advertised characteristics in all respects.

WATCH ROOM: A room immediately below the lantern room or service room where fuel and other supplies were kept where the keeper prepared the lanterns for the night and often stood watch. The clockworks (for rotating lenses) were also kept there.

WHISTLE: A wave actuated sound signal on buoys 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.

WINTER LIGHT: A light which is maintained during those winter months when the regular light is extinguished. It is of lower candlepower than the regular light but usually the same characteristic.


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