The Light House of Alexandria, built in 280 BC, is believed to be the oldest lighthouse. In the seventeenth century, lighthouse construction took on a swift pace in western and northern Europe. Britain's Trinity House constructed its first lighthouse in 1619. Boston Light on Little Brewster Island, built in 1716, was the first lighthouse in America. The oldest existing lighthouse in America is the Sandy Hook Lighthouse in New Jersey, built in 1764. The United States Coast Guard took over lighthouses in 1939. The earliest lighthouses used oil wick lamps or flames. They were replaced by electric lamps and more recently by solar-powered batteries.
The height of the light source is calculated taking into account the height of the tower, distance from the horizon in nautical miles and fog. A bright light is seen at intermittent intervals. The time interval is characteristic of a particular lighthouse and navigators can identify their location by observing the light pattern. To help differentiate between safe waters and dangerous shoals, sector lights with red or green filters may also be used. With the advent of electronic navigational aids like the GPS, ships have come to rely on light houses to a lesser degree.
Lighthouses differ to some extent based on location, period of construction and purpose. But certain features are common to most. The lantern room is a glass enclosure at the top of the light house tower. It holds the lamp, or the lens. Light beams out from here. The ventilator, located above the lantern room, is used to remove smoke and heat generated by lamps within the glass enclosure. The lightning rod is connected to the cupola roof to ensure that electricity from lightning is safely carried to the earth. The watch room is where the keeper keeps watch and prepares the lanterns. It holds fuel, supplies, clocks and equipment. The gallery is an open platform, located outside the watch room or the lantern room, used to clean the outside of the windows. The light station includes the light house tower and the other exterior buildings--keeper's living quarters, fuel house, boathouse and fog-signaling building.
Originally, lighthouses were constructed on solid rock or land. These onshore lighthouses were not always effective, especially, when they had to warn ships of a dangerous shoal located offshore. So, a lightship or a lighted buoy was used. Onshore lighthouses were built out of wood, stone masonry, cast-iron plate, brick, iron and steel and reinforced concrete. In some locations, such as river deltas, the land is too soft and unstable for onshore light houses. Chesapeake Bay, coral reefs off the Florida Keys and Delaware Bay are examples. Here, advanced technology that makes use of screw pile, caisson, pier/breakwater or skeletal tower lighthouse construction is employed to build offshore lighthouses.
Lighthouses help small fishing communities. The light guides fishermen in and out of the waters. Since more fish come out at night, lighthouses benefits the economy of small communities. Lighthouses that are popular tourist destinations like Cape Hatteras and Barnegat Lighthouse, have a positive impact on local economy. They also have historical value. The material used and the technique of lighthouse construction are representative of the period in which it was constructed. John Smeaton, the Stevenson family, Alexander Mitchell, and other lighthouse builders are known for their distinctive techniques and the challenges they faced in constructing lighthouses.
