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A Fresnel lens ( / ˈfreɪnɛl, - nəl / FRAY-nel, -nəl; / ˈfrɛnɛl, - əl / FREN-el, -əl; or / freɪˈnɛl / fray-NEL[ 1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
A zone plate is a device used to focus light or other things exhibiting wave character. [ 1] Unlike lenses or curved mirrors, zone plates use diffraction instead of refraction or reflection. Based on analysis by French physicist Augustin-Jean Fresnel, they are sometimes called Fresnel zone plates in his honor.
The tower is circular, and is 49 feet (15 m) in height, with the beacon at 83 feet (25 m) above sea level. The light, magnified by a third-order Fresnel lens, has a range of 18 miles (29 km). The tower is built of brick, and painted in alternating horizontal red and white stripes. A small gabled entry vestibule, also brick, projects from the tower.
The new all-white lighthouse tower was completed in 1868, receiving a first-order Fresnel lens made by Henry-Lepaute and Company of Paris, France that was first lit on May 10, 1868. [ 1 ] [ 6 ] The lower three levels of the tower served as the living quarters for the keepers and his assistants complete with kitchen, living room and bedrooms.
The simplest Fresnel zone plate antenna is the circular half-wave zone plate invented in the nineteenth century. The basic idea is to divide a plane aperture into circular zones with respect to a chosen focal point on the basis that all radiation from each zone arrives at the focal point in phase within ±π/2 range.
On May 15, 1874, the Gay Head Light was changed from flashing white to "three whites and one red" to differentiate the light from the area's two other principal lights located at Sankaty Head and Montauk Point. All three lights had Fresnel lenses, however, the Gay Head Light was the only light of the 1st Order.
In its developed form, the OLS consists of a horizontal row of green lights, used as a reference, and a column of vertical lights. The vertical lights signal whether the aircraft is too high, too low, or at the correct altitude as the pilot descends the glide slope towards the carrier's deck. Other lights give various commands and can be used ...
Little is known of the first front range light. In 1879 a new front range beacon was erected 448 feet (137 m) southeast of the light tower. This light, known as the Pensacola Bar Beacon, was a square pyramidal wooden tower, 26 feet (7.9 m) tall, sitting on a point 29 feet (8.8 m) above sea level, so that the light was 55 feet (17 m) above the ...