Sunglasses
Sunglasses or sun glasses 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.
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 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
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, 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" 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, "shell spectacles" to protect against sunlight on long marches, or by the British T. Longmore reporting in The Optical Manual 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
was the first to argue for UV protection with 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
Sunglasses offer protection against excessive exposure to light, including its visible and invisible components.The most widespread protection is against ultraviolet radiation, which can cause short-term and long-term ocular problems such as photokeratitis, cataracts, pterygium, and various forms of eye cancer. Medical experts advise the public on the importance of wearing sunglasses to protect the eyes from UV; for adequate protection, experts recommend sunglasses that reflect or filter out 99% or more of UVA and UVB light, with wavelengths up to 400 nm. Sunglasses that meet this requirement are often labeled as "UV400". This is slightly more protection than the widely used standard of the European Union, which requires that 95% of the radiation up to only 380 nm must be reflected or filtered out. Sunglasses are not sufficient to protect the eyes against permanent harm from looking directly at the Sun, even during a solar eclipse. Special eyewear known as solar viewers are required for direct viewing of the sun. This type of eyewear can filter out UV radiation harmful to the eyes.
More recently, high-energy visible light has been implicated as a cause of age-related macular degeneration; before, debates had already existed as to whether "blue blocking" or amber tinted lenses may have a protective effect. Some manufacturers already design glasses to block blue light; the insurance company Suva, which covers most Swiss employees, asked eye experts around Charlotte Remé to develop norms for blue blocking, leading to a recommended minimum of 95% of the blue light. Sunglasses are especially important for children, as their ocular lenses are thought to transmit far more HEV light than adults.
Assessing protection
The only way to assess the protection of sunglasses is to have the lenses measured, either by the manufacturer or by a properly equipped optician. Several standards for sunglasses allow a general classification of the UV protection, and manufacturers often indicate simply that the sunglasses meet the requirements of a specific standard rather than publish the exact figures.One "visible" quality test for sunglasses is their fit. The lenses should fit close enough to the face that only very little "stray light" can reach the eye from their sides, or from above or below, but not so close that the eyelashes smear the lenses. To protect against "stray light" from the sides, the lenses should fit close enough to the temples or merge into broad temple arms or leather blinders. Another test is for lenses said to be polarising: having two such lenses, they should block all light when after each other with one pair turned 90°.
It is not possible to "see" the protection that sunglasses offer. Dark lenses do not automatically filter out more harmful UV radiation and blue light than light lenses. Inadequate dark lenses are even more harmful than inadequate light lenses because they provoke the pupil to open wider. As a result, more unfiltered radiation enters the eye. Depending on the manufacturing technology, sufficiently protective lenses can block much or little light, resulting in dark or light lenses. The lens color is not a guarantee either. Lenses of various colors can offer sufficient UV protection. Regarding blue light, the color gives at least a first indication: Blue blocking lenses are commonly yellow or brown, whereas blue or gray lenses cannot offer the necessary blue light protection. However, not every yellow or brown lens blocks sufficient blue light. In rare cases, lenses can filter out too much blue light, which affects color vision and can be dangerous in traffic when colored signals are not properly recognized.
High prices cannot guarantee sufficient protection as no correlation between high prices and increased UV protection has been demonstrated. A 1995 study reported that "Expensive brands and polarizing sunglasses do not guarantee optimal UVA protection." The Australian Competition & Consumer Commission has also reported that "onsumers cannot rely on price as an indicator of quality". One survey even found that a $6.95 pair of generic glasses offered slightly better protection than expensive Salvatore Ferragamo shades.