Reflected ray: The ray of light which is sent back by the mirror from the point of incidence is called reflected ray. Beyond one mile, the light from the various lamps would have blended in the eye of the mariner and become a single light, eliminating the ability to establish the lighthouse’s characteristic. The mariners had complained they could not see the coal fire in the lighthouse from more than a few miles away. (1782). This is why plane mirror is made by depositing a thin layer of silver metal on one side of a plane glass sheet. However, plain copper was not a very reflective surface and was soon abandoned. The parabolic shape was very difficult to fashion by hand. Osnaghi’s design was called the ‘Parabolic Reflector for Intermittent Lights,’ and was specifically designed for use with the electric-arc lamp. lamps, because most of the reflected light was lost when it returned and was blocked by the nearly opaque mantle and by the large burners. (1860). The holophotal reflector-lens combination was first installed at the North Harbor light at Peterhead, Scotland. Beginning in late 1909, Raymond Haskell, Assistant Superintendent of the Third District Depot, began developing the spherical-glass mirror reflector-lens combination. A flat plate reflector reflects light in many directions and only a small portion of the light is reflected forward in a direction useful to a mariner. In addition, some of the light is lost around the edge of the reflector and it was determined that only 70 percent of the total light from the lamp was actually collected by the reflector. Lens with Spherical Doubly Reflecting Prisms. It was named the ‘Spangle Light’ because of its use of a concave drum on which 4000 glass mirror facets were placed. By accident, the Winslow Lewis design, where the flame was too far forward of the reflector focus, actually helped to allow more of the reflected light to be used. (1807). What makes them that way is that some of the electrons in these metals can move around very very easily. In his book 'A Treatise on Practical Seamanship' published in 1777, William Hutchinson described how his reflectors were constructed and employed: We have had in use here at Liverpool, reflectors of 1, 2, and 3 feet focus, and 3, 5½, 7½ and 12 feet diameter, the three smallest made of tin plates soldered together, and the largest of wood, covered with plates of looking glass, fixed as near as can be to the parabolic curve, and using a copper lamp. Lighthouse designers were constantly looking for ways to produce more light. Winslow Lewis also produced lamps with larger reflectors, which were mounted differently and had oil level adjusting screws on the chandelier in a mounting plate behind the lamp fountain, as shown below. It's from the Greek word (Catoptron) for mirror, or reflection, and the lighthouse illumination system based on the principle of reflection was given the name Catoptric System in English. Angle of reflection: The angle made by the reflected ray with the normal at point of incidence is called angle of reflection. Each of the reflecting surfaces had a central hole where the lamp flame was placed. The Spangle Light used at Lowestoft Lighthouse. Silver metal is the best reflector of light. This combination collected nearly all of the available light and was used in harbor and range lights. He also suggested that the reflectors could be stacked, as on a staircase, in different numbers at each lighthouse to provide a form of characteristic to distinguish one lighthouse from another. One thumbscrew was used to firmly attach both the lamp and the reflector to the chandelier. Many different kinds of metal are shiny. Therefore the right side of our body becomes the left side in its image and the left side of our body becomes the right side in its image in mirror. Braun was given a patent for the use of these reflectors in lighthouses, in 1681. 1810-1818. (1811). It is explained below in the figure. Angle of incidence: The angle made by the incident ray with the normal is called angle of incidence. In 1790, Borda had Monsieur Lenoir, a young artist of Paris, create true parabolic thirty-one-inch diameter reflectors, made of steel and clad with four leaves of silver, based on Teulere’s design, using Argand style lamps made by Antoine Quinquet without chimneys, and had him install them in the Cordouan lighthouse in France. The design was developed just as the Fresnel lens came into use and the ‘Fanal a Double Aspect’ was never actually used in lighthouses. This three-split mirror combination replaced the doubly reflecting prisms previously discussed in lenses where the otherwise useless light on the landside of the lens could be collected. Thus the left half of the split mirror would focus to the left of center and the right half would focus to the right. Problems with the manufacture of reflectors kept them from reaching their theoretical capabilities. It also had a 3.3-inch plano-convex lens to concentrate the light. The earliest known use of these reflectors was on the Baltic Sea at the lighthouse of Gollenberg, now in Poland, which had a single candle lamp backed by a polished metal reflector in 1532. In this design, a Fresnel lens was modified with a prism panel removed and replaced with a spherical mirror designed to reflect the light back upon the flame in the focus of the lens and then out through the lens prism panel opposite the mirror. Later, Fresnel also used mirrors with a slight parabolic curve to improve his design. The result of this split mirror design brought the reflected light back toward the flame, but beside the mantle and burner, thus increasing the light. The upper searchlight was discontinued after World War II, and used only as an emergency backup. One of the more unusual reflector designs was invented about 1687 and used at the lighthouse of Orskar, in Sweden, which had 6 large Braun reflectors, shape unknown, each with 2 oil lamps. The lamp in Walker’s reflectors used a single flat wick made of five cotton strands. During the 1770s, William Hutchinson designed a dual tin reflector with a lamp having a single reservoir and two wick tubes utilizing rough rope wicks. In Germany this lighthouse was known as the ‘Schnellblitzfeuer’ or very quick flashing light. A third reflector was added behind the focus inside one of the reflector halves and facing the lamp. A very common example of this technique is the traditional umbrella reflector, invented by George Larson [4] , typically having a gold, silver or matte white interior onto which a lamp fitted with a circular reflector is projected, providing a broad, soft illumination. Point of incidence: The point at which the incident ray falls on the mirror surface is called point of incidence.