Sunglasses or sun glasses are a form of protective eyewear that usually enclose or protect the eye pupil in order to prevent strong light, ultraviolet (UV) rays, and increasingly, blue light ("blue blocking") from penetrating. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist which feature lenses that are colored, polarized or darkened. In the early 20th century they were also known as sun cheaters ( cheaters being an American slang term for glasses).
Many people find direct sunlight too bright for comfort. During outdoor activities, the human eye can receive more light than usual. Healthcare professionals recommend eye protection whenever outside to protect the eyes from ultraviolet radiation and blue light, which can cause several serious eye problems. Sunglasses have long been associated with celebrities and film actors primarily from a desire to hide or mask their identity. Since the 1940s sunglasses have been popular as a fashion accessory, especially on the beach.
History
Precursors
It is said that the Roman emperor Nero liked to watch gladiator fights with emeralds. These, however, appear to have worked rather like mirrors. Flat panes of smoky quartz which offered no corrective powers but did protect the eyes from glare were used in China in the 12th century or possibly earlier. Contemporary documents describe the use of such crystals by judges in Chinese courts to conceal their facial expressions while questioning witnesses..
James Ayscough began experimenting with tinted lenses in spectacles in the mid-18th century, around 1752. These were not "sunglasses" as such; Ayscough believed blue- or green-tinted glass could correct for specific vision impairments. Protection from the sun's rays was not a concern for him.
Yellow/amber and brown-tinted spectacles were also a commonly-prescribed item for people with syphilis in the 19th and early 20th centuries because sensitivity to light was one of the symptoms of the disease.
In prehistoric and historic time, Inuit peoples wore flattened walrus ivory "glasses," looking through narrow slits in order to block the harmful reflected rays of the sun.
Modern developments
In the early 1900s, the use of sunglasses started to become more widespread, especially among the pioneering stars of silent movies. It is commonly believed that this was to avoid recognition by fans, but the real reason was they often had perennially red eyes from the powerful arc lamps that were needed due to the extremely slow speed film stocks used. The stereotype persisted long after improvements in film quality and the introduction of ultraviolet filters had eliminated this problem. Inexpensive mass-produced sunglasses were introduced to America 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.
Polarized sunglasses first became available in 1936, when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter.
Functions
Visual clarity and comfort
Sunglasses can improve visual comfort and visual clarity by protecting the eye from glare.
Various types of disposable sunglasses are dispensed to patients after receiving mydriatic eye drops during eye examinations.
The lenses of polarized sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces such as water. They are popular among fishermen because they allow wearers to see into water when normally only glare or reflected light would be seen.
Protection
Sunglasses offer protection against excessive exposure to light, including its visible and invisible components.
The most widespread protection is against ultraviolet radiation (UV), which can otherwise cause short-term and long-term ocular problems such as photokeratitis, snow blindness, 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 99-100 % of UVA and UVB light, with wavelengths up to 400 nanometers (nm). Sunglasses which meet this requirement are often labeled as "UV 400." This clearly exceeds the widely used standard of the European Union (see below), which requires only 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.
More recently, high-energy visible light (HEV) 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 to block blue light; the insurance company Suva, which covers most Swiss employees, asked eye experts around Charlotte Remé (ETH Zürich) 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 (lenses "yellow" with age).
There has been some speculation that sunglasses actually promote skin cancer. This is due to the eyes being tricked into producing less melanocyte-stimulating hormone in the body.
Assessing the protection of sunglasses
The only way to assess the protection of sunglasses is to have the lenses measured, either by the manufacturer or by an optician with the necessary equipment. Several standards for sunglasses (see below) allow a general classification of the UV protection (but not the blue light protection), and manufacturers often indicate simply that the sunglasses meet the requirements of a specific standard rather than publish the exact figures.
The only "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 and/or merge into broad temple arms or leather blinders.
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 as compared to light lenses. Inadequate dark lenses are even more harmful than inadequate light lenses (or wearing no sunglasses at all) because they provoke the pupil to open wider; as 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 lense color is not a guarantee either: Lenses of various colors can offer sufficient (or insufficient) 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 lense blocks sufficient blue light; and in rare cases, lenses can even filter out too much blue light (i.e., 100 %), which affects color vision and can, for example, be dangerous in traffic when colored signals are not recognized well enough or at all.
In addition, 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 and 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 did expensive Salvatore Ferragamo shades.
Further functions of sunglasses
While non-tinted glasses are very rarely worn without the practical purpose of correcting eyesight or protecting one's eyes, sunglasses have become popular for several further reasons, and are sometimes worn even indoors or at night.
Sunglasses can be worn to hide one's eyes: They can make eye contact impossible, which can be intimidating to those not wearing sunglasses; the avoided eye contact can also demonstrate the wearer's detachment, which is considered desirable ("cool") in some circles. Eye contact can be avoided even more effectively by using mirrored sunglasses. In addition, sungla
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