Glossary of Lighthouse Terms

Argand Lamp  An oil lamp which was clean burning and produced an intense flame and a very bright light. Invented by Frenchman Ami Argand, this lamp was widely used during the late eighteenth and early nineteenth centuries.

Automatic Light  A lighthouse with no keepers. The lights are controlled by remote control, timers or light and fog detectors.

Beacon  A light or radio signal.

Bug Light  see Caisson Towers

Caisson Towers  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 Towers  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 sight for erection.

Characteristic  The identifying feature of a lighthouse.  To distinguish one lighthouse from another, each lighthouse is given a distinct color and/or pattern of flashes of the light.

Clamshell lenses  Rather than being round as most lenses are the Clamshell, or Bivalve, lenses has a flattened shape reminiscent of a clam shell. The usually have two bulls 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.

Coffee Pot Light  see Caisson Towers

Cottage Style  A lighthouse comprised of a small one story building with a light on top. The building housed the keepers, were relatively inexpensive to build and maintain.

Daymark  The color or pattern and shape of navigational aid used to identify it during daylight hours.

Fixed Signal  A beacon light that shines constantly during its hours of operation.
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 know as the height of the focal plane.

Flashing Signal  A beacon light that seems to flash on and off. Each light has a set pattern of flashes to distinguish it from other lights.

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 know as the height of the focal plane.

Fog Horn or Fog Signal  The sound, usually a horn, siren or trumpet, produced to warn ships away from obstacles during fog or poor visibility.

Fresnel Lens  (Freh-nell)  A lens made up of a group of hand polished glass prisms mounted in a brass frame.  They were invented by French physicist Augustin Fresnel. They project a powerful beam of light which can be seen from great distances. They range is size from a 1st order lens, which can be up to 12 feet tall and 6 feet in diameter, down to a 6th order lens, which is only about a foot tall.

Gallery  A walkway with railing that encircles the lantern. This enabled the keepers to maintain the outside of the lamp house.

Harbor Light  A light to guide ships safely into a harbor.

Lamp and Reflector  A lamp and highly polished mirror used before the invention of the Fresnel lens.

Lantern  The glass enclosure at the top of a lighthouse which houses the lamp and lens.

Light Station  A navigational aid with a light beacon.  A light station may or may not include a tower, keepers quarters or fog signal.

Light Tower  A tall structure used to elevate a light beacon so that mariners may see it at a distance.

Lighthouse  A term applied to a variety of structures built to aid in guiding ships.  The term is often used interchangeably with "light tower" or "light station".

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.

Modern Optic  Term applied to a broad range of light weight, weatherproof beacons used in modern devises.

Occulting Light  A light that is partially blocked, or occulted, to make it appear to flash.  Also called an eclipsing 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.

Range Lights  Lights that are displayed in pairs to guide ships through a narrow channel. The rear range light will be the taller of the two, with the front range light often at waters edge. When the ship is in the 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.

Screw-pile Towers  Lighthouse built on piles that were "screwed" into the water bottom.  They often supported a small wooden building with a tower and light on top.

Skeleton Towers  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.

Spark Plug Light  See Caisson Towers

Twin Light  A few lights used to consist of two separate lights to distinguish them from nearby lights.