The Physics
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Power of a Lighthouse

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Fox, Fred. Automation as applied to various lighthouses. 12 June 2005. "Maughold Head lighthouse… Final gear driveThe decision was taken to retain the existing lens and motorise the drive ie.bypass the clockwork drive. To retain the 250 watt Multi-vapour lamp but add a lampchanger." 500 W
Welcome… to the Rose Island Lighthouse… 'A guiding light to conservation' Rose Island Lighthouse Foundation. 12 June 2005. "Wind supplies 90% of our electric needs from a Bergey 1500 windmill. After a few calm days, the keeper runs the 5KW diesel generator to recharge the 24-Volt, lead-acid, 'solar” battery bank. The whole lighthouse, including the beacon, runs on one 20 AMP service." < 480 W
Nobska Light, a shining beacon in storm tossed seas. Falmouth Amateur Radio Association of Cape Cod, Massachusetts. 21 August 2003. "A close up view of the current light source, a 250 watt halogen bulb." 250 W
Cap Cod (highland) Light Station. New England Lighthouse Wallpaper Guide. 2004. "The Fourth-order Fresnel Lens illuminated by a 1000-watt electric bulb…." 1000 W
Brief History of Lighthouses in NZ. Maritime Safety of New Zealand. 10 June 2005. "A typical New Zealand lighthouse has a lens that revolves around a 1,000-watt bulb. 1000 W

A lighthouse is a tower with an extremely strong light that serves as a navigation aid for marines. Lighthouses help sailors determine their position, inform them that land is near, and warn them of dangerous rocks and reefs.

Lighthouses were introduced thousands years ago by the ancient Egyptians. They lit fires on top of hill to guide ships out in the sea. Then the Romans built lighthouses at a number of ports. They soon established towers with an ongoing light. The beam of those towers was most likely produced by a system of multiple flames and mirrors.

Each lighthouse gives off a specific light pattern. There are five types of patterns:

  1. Fixed-is a steady beam.
  2. Flashing- has periods of darkness longer than periods of light.
  3. Occulting- periods of light are longer than its periods of darkness.
  4. Group flashing-light gives off two or more flashes at regular intervals.
  5. Group occulting- light consists of a fixed light with two or more periods of darkness at regular intervals.

The patterns can be matched up with a location on a recorded publication called a light list available to marines. In the day time lighthouses are identified by their shape and color patterns.

Lighthouses project light though a special lens that increases the intensity of the light from their lamps. The lens is called Fresnel lens; it was invited in 1822 by Augustin Fresnel, a French physicist. Each face of a Fresnel lenses is surrounded by a ring of triangular prism, which refract and focuses the light. Some Fresnel lenses measure as much as 8 (2.4 meters) feet in height and 6 feet (1.8 meters) in diameter. The distance the light can be see is up to 20 miles in clear weather, but in cases of haze, smoke, rain, fog and snow can dramatically affect the visibility. For such cases many lighthouses contain foghorns, bells or other sound making devices. Today, many lighthouses contain a radio beacon, which sends out radio signals that are picked up by shipboard radio direction finders.

Today, after the development of advanced electronic navigation aids the number of lighthouses in use declined. The number of lighthouses in use around the world is only about 1,400.

The power of the bulb used in a lighthouse depends on the type of the bulb used. Many of the lighthouses have 1,000 watt bulbs, but today a 250 watts halogen bulb replaces a 1,000 watt tungsten bulb.

Daria Zainullina -- 2005