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Light houses are a tower, construction, or other type of structure designed to emit light from a system of lamps and lenses and used as an aid to navigation offshore or on inland waterways.
Lighthouses mark life threatening coastlines, hazardous shoals , reefs , safe entries to harbors, and can also aid in aerial navigation. Once widely used, the amount of functional lighthouses has declined due to the expense of maintenance and replacement by modern electronic navigational systems.
In light houses, the generator of light is called the "lamp" (whether electric or fueled by oil) and the concentration of the light is by the "lens" or "optic". Earlier lit by open fires and later on candles, the Argand hollow wick lamp and parabolic reflector followed produced around 1781 in Europe and deployed on the Cordouan lighthouse in France in 1782, with a revolving element being added in 1790.
In the U.S., whale oil was used with wicks as the source of light until the Argand parabolic reflector system was brought in around 1810 by Winslow Lewis. Colza oil superseded whale oil in the early 1850s, but U.S. farmers' lack of interest in growing this caused the service to switch to lard oil in the mid-1850s. Kerosene began replacing lard oil in the 1870s and the lighthouse service was finally changed over by the late 1880s.
Electrical energy and carbide (acetylene gas began superseding kerosene about the turn of the 20th century.Carbide was upgraded by the Dalén light which automatically lit the lamp at dusk and extinguished it at the break of day.
Prior to advanced strobe lights, lenses were used to concentrate the light from a uninterrupted source. Vertical light rays of the lamp are redirected into a horizontal plane, and horizontally the light is focused into one or a few directions at a time, with the light beam swept around.
As a consequence, in addition to seeing the side of the light beam, the light is directly visible from long distances, and with an identifying light characteristic . This concentration of light is achieved with a circumvolving lens assembly. In former lighthouses, the light source was a kerosene lamp or, originally, animal or vegetable oil Argand lamp, and the lenses rotated by a weight driven clockwork assembly wound by lighthouse keepers, usually as often as every two hours.
The lens assembly sometimes floated in liquid mercury to bring down friction. In more modern lighthouses, electric lights and motor drives were applied, normally powered by diesel electric generators. These also provided electricity for the lighthouse keepers.
Efficiently concentrating the light from a huge omnidirectional light source and calls for a very large diameter lens. This would call for a very thick and heavy lens system if a conventional lens were applied. The invention of the Fresnel lens (pronounced in 1822 by French physicist Augustin-Jean Fresnel revolutionized light houses in the 19th century, focusing 85% of a lamp's light versus the 20% focused with the parabolic reflectors of the time. Its invention enabled construction of lenses of large size and short focal length without the weight and volume of material in conventional lens designs.
Though the Fresnel lens was invented in 1822, it was not in use in the U.S. until the 1850s due to the parsimonious administrator of the United States lighthouse establishment, Stephen Pleasonton . With the founding of the United States Lighthouse Board in 1852, all U.S. lighthouses received Fresnel lenses by 1860.
Fresnel lenses are graded by order, a measure of refracting power, with a first order lens being the largest, most powerful and expensive; and a sixth order lens being the smallest. The order is based on the focal length of the lens. A first order lens has the longer focal length, with the sixth being the shortest. Coastal lighthouses commonly use first, second, or third order lenses, while harbor lights and beacons use fourth, fifth, or sixth order lenses.
A few lighthouses, such as those at Cape Race , Newfoundland, and Makapuu Point , Hawaii, used a more powerful hyperradiant Fresnel lens constructed by the firm of Chance Brothers . In recent times, a lot of Fresnel lenses have been superseded by revolving aerobeacons which call for less maintenance. In modern automated lighthouses, this system of revolving lenses is frequently replaced by a high intensity light that emits brief omnidirectional flashings (concentrating the light in time instead of direction). These lights are similar to obstruction lights used to warn aircraft of tall structures.
Recent innovations are "Vega Lights", and initial experimentation's with light-emitting diode (LED) panels.
In any of these designs an observer, instead of watching a uninterrupted weak light, sees a more brilliant light during short time intervals. These split second* of bright light are arranged to produce a light characteristic or, pattern unique to a lighthouse.
For instance, the Scheveningen Lighthouse flashes are alternately 2.5 and 7.5 seconds. A few lights have sectors of a specific color (generally formed through colored panes in the lantern) to identify safe water areas from dangerous shoals. Advanced lighthouses frequently have got unique reflectors or Racon transponders so the radar signature of the light is likewise unique.
Lighthouse lantern room from mid-1800s While lighthouse buildings differ dependant on the positioning and purpose, they tend to have standard components. A light station comprises the lighthouse tower and all outbuildings, such as the keeper's living quarters, fuel house, boathouse, and fog-signaling building. The Lighthouse itself comprises of a tower construction supporting the lantern room where the light functions.
The lantern room is the glassed-in housing at the top of a lighthouse tower bearing the lamp and lens. Its glass storm panes are underpinned by metal Astragal bars running vertically or diagonally. At the top of the lantern room is a protected ventilator designed to transfer the smoke of the lamps and the heat that builds in the glass enclosure.
A lightning rod and grounding system attached to the metal cupola roof supplies a safe conduit for any lightning strikes. Directly below the lantern room is normally a Watch Room or Service Room where fuel and additional supplies were kept and where the keeper set up the lanterns for the night and frequently stood watch.
The clockworks (for revolving the lenses) were also situated there. On a lighthouse tower, an open platform known as the gallery is frequently placed outside the watch room (called the Main Gallery) or Lantern Room (Lantern Gallery). This was primarily used for cleaning the exterior of the windows of the Lantern Room.
Light houses neighboring to each other that are similar in shape are frequently painted in a unique pattern in order they can easily be distinguished during daylight, a marking known as a daymark . The black and white barber pole spiral pattern of Cape Hatteras Lighthouse s one example. Race Rocks Light in western Canada is painted in horizontal black and white bands to stand out against the visible horizon.
Range Lights in Nantucket, Massachusetts , showing the observer is left of the desired channel aligning two fixed points on land furnishes a navigator with a line of position called a range in the U.S. and a transit in Britain. Ranges can be used to accurately line up a vessel inside a narrow channel such as in a river.
With landmarks of a range illuminated with a set of fixed lighthouses, nighttime navigation is possible. Such twinned lighthouses are named range lights in the U.S. and leading lights in the United Kingdom. The closer light is referred to as the beacon or front range; the furthest away is known as the rear range. The rear range light is nearly always taller than the front.
Once the vessel is on the precise course, the two lights align vertically. But once the observer is out of position, the difference in alignment indicates the proper direction of travel to adjust the course.
Model light houses are a perfect nautical gift for any mariner.
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