Sunglasses or sun glasses (informally called shades or sunnies; more names below) are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that are colored, polarized or darkened. In the early 20th century, they were also known as sun cheaters (cheaters then being an American slang term for glasses). Since the 1930s, sunglasses have been a popular fashion accessory, especially on the beach. The American Optometric Association recommends wearing sunglasses that block ultraviolet radiation (UV) whenever a person is in the sunlight to protect the eyes from UV and blue light, which can cause several serious eye problems. Their usage is mandatory immediately after some surgical procedures, such as LASIK, and recommended for a certain time period in dusty areas, when leaving the house and in front of a TV screen or computer monitor after LASEK. Dark glasses that do not block UV radiation can be more damaging to the eyes than not wearing eye protection at all, because they tend to open the pupil and allow more UV rays into the eye.
History
First precursors
Since the 13th century and until the spread of contemporary UV-shielding spectacles against snowblindness, Inuit made and wore snow goggles of flattened walrus or caribou ivory with narrow slits to look through to block almost all of the harmful reflected rays of the sun. In many different forms and with many different materials, the indigenous peoples of North America and northern Asia crafted highly efficient equipment to protect their eyes against the damaging effects of strong sunlight in icy circumstances.
Other precursors Pliny the Elder claimed that the Roman emperor Nero liked to watch gladiator fights using cut emeralds. These, however, appear to have worked rather like mirrors. The first sunglasses, made from flat panes of smoky quartz called Ai Tai (靉靆), meaning "dark clouds," which offered no corrective powers but did protect the eyes from glare, were used in China in the 12th century or possibly earlier. Documents describe the use of such crystal sunglasses by judges in ancient Chinese courts to conceal their facial expressions while questioning witnesses. In 1459, Nuno Fernandes made a request for a pair of spectacles to protect the eyes while horseriding in the snow against the glare coming from the snow, though no description of any actual spectacles is given. King Louis XIV's court watched the 1706 solar eclipse through a telescope with a smoky glass filter attached. By the 18th century, tinted, mirror-like framed Murano glasses had been used as so-called "gondola glasses" (vetri da gondola and also da dama) by Venetian women and children, to shield their eyes from the glare from the water in the canals. The Doge and other well-off Venetians, such as possibly Goldoni, sported, in the late 18th century, so-called "goldoni glasses," tinted pairs of spectacles with pieces of cloth as sun guards on the sides of the glasses. James Ayscough began experimenting with tinted lenses in spectacles around 1752. These were not "sunglasses" as that term is now used; Ayscough believed that blue- or green-tinted glass could correct for specific vision impairments. Protection from the sun's rays was not a concern for him.
One of the earliest surviving depictions of a person wearing sunglasses is one from 1772 of the scientist Antoine Lavoisier, who worked with amplified sunlight. By the 19th century, tinted spectacles were worn by railway travelers. Popularly, it is claimed that yellow/amber and brown-tinted glasses had been used to alleviate symptoms of syphilis in the 19th and early 20th centuries, because sensitivity to light was one of the symptoms of the disease, although no sources have been found that state prescription of such. From the late 19th century, short references of sunglasses have been found in reports, such as one from 1866 by Walter Alden, who wrote of soldiers using, during the American Civil War (1861–1865), "shell spectacles" ("verres de cocquille") to protect against sunlight on long marches, or by the British T. Longmore reporting in The Optical Manual (1885) of soldiers in Egypt being equipped with tinted glass "eye protectors." By 1895, sunglasses were mentioned in advertisements, such as in The Sioux City Journal.
Modern developments Jean-Marie-Théodore Fieuzal (1836–1888) was the first to argue for UV protection with (yellow) shaded glasses, and by 1899, Rodenstock GmbH produced possibly the first sunglasses intended for shielding eyes from UV light and not just glare. In 1913, Crookes lenses were introduced, made from glass containing cerium, which completely blocked ultraviolet light. In the early 1920s, the use of sunglasses started to become more widespread, especially among movie stars. Inexpensive mass-produced sunglasses made from celluloid were first produced by Sam Foster in 1929. Foster found a ready market on the beaches of Atlantic City, New Jersey where he began selling sunglasses under the name Foster Grant from a Woolworth on the Boardwalk. By 1938, Life magazine wrote of how sunglasses were a "new fad for wear on city streets ... a favorite affectation of thousands of women all over the U.S." It stated that 20 million sunglasses were sold in the United States in 1937 but estimated that only about 25% of American wearers needed them to protect their eyes. At the same time, sunglasses started to be used as aids for pilots and even produced for the gaining aviation sector, eventually adding to sunglasses as cultural icons and to their popularity. Polarized sunglasses first became available in 1936 when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter. In 1947, the Armorlite Company began producing lenses with CR-39 resin. As of 2008, Xiamen, China, was the world's largest producer of sunglasses with its port exporting 120 million pairs each year.
Functions
Visual clarity and comfort Sunglasses can improve visual comfort and visual clarity by protecting the eye from glare. The lenses of polarized sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces, such as water. They allow wearers to see into water when only surface glare would otherwise be seen, and eliminate glare from a road surface when driving into the sun.
Protection
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