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Barnegat Lighthouse's first-order Fresnel lens was made in 1856 by Henri LePaute of Paris, France, from glass made at the famous Furnace at St. Gobian. The beehive shaped lens, which was six feet in diameter and 12 feet high, was formed from 1,024 separate glass prisms mounted in bronze fittings. The three ton lens was delicately balanced on heavy bronze rollers. The entire lens could be rotated by the pressure of one finger. This lens is on display in the Barnegat Light Museum on Central Avenue and 5th Street in Barnegat Light, New Jersey.
The mechanism that rotated the light worked like a grandfather clock. A 150 pound weight hung on a 65 foot steel cable which was threaded down the center pipe. The mechanism had to be wound once a day. The lens made one complete rotation every four minutes. The rotation of the lens caused the fight to flash every ten seconds. The time between flashes and other traits were known as a lighthouse's "characteristic." Barnegat Lighthouse's characteristic was a single light which flashed every ten seconds at all points of the compass.
Fresnel lenses were classified into several orders depending on size and power. The location and importance of a particular lighthouse determined which order lens was placed there. A first-order lens was used in major navigational aids, like Barnegat, while the slightly smaller second-order would be used for coastal landfalls where the intensity of the larger lens was not necessary. At harbor entrances, inlets large bays, or lakes, a third-order lens would be positioned, while the smaller fourth and fifth-orders were used as range lights or as leading lights. The smallest sixth-order lights were used to mark shoals, bays, and channels. Eventually the Lighthouse Service used 3 1/2 and 6 1/2 order lenses and the extremely powerful Hyper-radial first order. Makapuu, Hawaii was one of the few lighthouses in the United States that used this last lens type.
The order of lenses is no longer as important as it once was. Many of the classical Frensel lenses have been removed from the lighthouses. Some modern lighting devices still rely on Frensel's-principles and design, but make use of plastics and modern light bulbs. Mariners now have a variety of methods available to them to navigate, including satellite, radar and other electronic equipment.
The above information
was taken from a brochure put out by:
N.J. Department of Environmental Protection and Energy
Division of Parks & Forestry