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Lighthouses were designed to help sea goers navigate their vessels safely back to shore. There are several ways of doing this through lights, sounds, shapes and colors. The following information explains the basics of aids to navigation. |
The effectiveness of a visual aid to navigation depends on visibility and identification - a mariner must be near enough to see it, and he must be absolutely certain as to which one he sees.
Range of visibility of a light in clear weather depends upon two factors - its intensity and its height above the water. An electric light is visible farther than a candle, because its intensity is greater. In the daytime, intensity makes very little difference; recognition depends on shapes and color contrasts. By day, as well as by night, the height of an object affects the distance at which it can be seen. Range of visibility also depends on the condition of the atmosphere; fog, rain, and snow reduce the range at which a light can be seen.
Identification Usually the problem is not so much to see the aid as it is to tell which aid you see. To help in this regard, aids have different shapes and colors for daytime identification, and variations in the light characteristics at night. These latter variations are obtained through the use of differences in color, and by showing for different periods of time. A light which is on for a short time, then off for a longer period, is called a "flashing light". If the time the light is on is equal to or exceeds the time it is off, the light is called "occulting". The period of darkness is called "eclipse". Light also have "equal-interval" and Morse code characteristics.
When the light is attended, there will frequently be a group of buildings around the tower for the fog signal and radiobeacon equipment and station personnel. Such a group of buildings constitutes a light station.
The flashing lights of lighthouses, bouys, and other aids to navigation are produced in several ways. In some large lights the flashes are produced by rotating lenses. Some electric lights are flashed by timers which break the current flow. In lights burning bottled gas, the flashes are made by cutting the flow of gas; each charge of gas is ignited at the burner by a pilot light.
All large lighthouses use electricity. Incandescent lamps produce as much as 5,000,000 candlepower where such brilliance is needed. Lenses of highly polished glass prisms are assembled in many types to produce the characteristics needed.
Glossary of Lighthouse Terms
Argand Lamp - A hollow wick oil lamp.
Astragal - Metal bars dividing the lantern room glass into sections.
Aton - Aids to navigation.
Bullseye - A convex lens used to concentrate (refract) light.
Characteristic - Individual flashing pattern of each light.
Crib - The part of the lighthouse structure between the tower and the foundation.
Daymark - Unique color scheme and/or pattern that identifies a specific lighthouse during daylight hours.
Ebbing - A tide falling or moving from high to low water.
Fixed Light - A steady, non-flashing beam.
Flooding - A tide rising or moving from low to high water.
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.
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 watchroom and/or lantern room.
Hollow - A concentric cotton wick used in Argand and other lamps.
Keeper - The person who takes care of the light in the lighthouse. (The head keeper is responsible for the operation of a light station.)
Lamp - The lighting apparatus inside a lens.
Lamplighters - Civilians who care for minor working lights.
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.
Lighthouse - A tower located at some place important or dangerous to navigation: it has a very bright light at the top, and often foghorns, sirens, etc., by which ships are guided or warned.
Lightship - A ship anchored at a charted position to mark a reef, shoal, or an important navigational point. They are painted bright red with a white superstructure, and they have their names in large white letters on their sides. At night a characteristic light is shown so the vessel is really a floating lighthouse.
Light Station - A complex containing the lighthouse tower and all of the outbuildings (the keeperšs living quarters, fuelhouse, boathouse, fog-signaling building, etc.).
Log - A book for maintaining complete daily records, similar to a diary.
Loran - Long range aids to navigation.
Navigation - The science of locating the position and plotting the course of a vessel.
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.
Parapet - The walkway around the outside of the lantern room.
Port Side Light - A red light on the left side of a vessel.
Prism - A transparent piece of glass that refracts or disperses light.
Range Lights - Two lights, located some distance apart, visible in one direction only. When a ship is steered so that one light is directly above the other, they will be in the marked channel.
Reflect - Bend or throw back light.
Refract - Bend or slant rays of light.
Revolving Light - One that produces a flash or characteristic.
SOS - A distress signal in Morse Code ( . . . - - - . . . ).
Spider Lamp - Shallow brass pan containing oil and several solid wicks.
Stag Light - A lighthouse with no family living in it (inhabited by men only).
Starboard Side Light - A green light on the right side of a vessel.
Tide - The regular rise and fall of the water level along a seacoast or in an ocean port. Gravitational attraction of the moon is the primary cause of tides. Since the moon orbits the earth every 24 hours and 50 minutes, the low and high tides are about 12 hours and 25 minutes apart.
Tower - Structure supporting the lantern room of the lighthouse.
Ventilator Ball - A ball shaped vent above the lantern room designed to remove excess heat and fumes and bring in fresh air.
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 located there.
Wick Solid - A solid cord used in spider lamps that draws fuel up to the flame by capillary action.
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