Sunglasses or sun glasses are a visual aid, variously termed spectacles or glasses, which feature lenses that are coloured or darkened to prevent strong light from reaching the eyes. In the early Twentieth century they were also known as sun cheaters (or simply cheaters).
Many people find direct sunlight too bright to be comfortable. 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, which can lead to the development of a cataract. 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.[1] 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.[2]
James Ayscough began experimenting with tinted lenses in spectacles in the mid-18th century. 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 of his.
Yellow/Amber and brown-tinted spectacles were also a commonly-prescribed item for people with syphilis in the 19th and early 20th centuries because of the sensitivity to light that was one of the symptoms of the disease.
In prehistoric and historic times, Eskimoan peoples wore flattened ivory "glasses," seeing through narrow slits, in order to block the harmful reflected rays of the sun.[3][4]
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[citation needed]. 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.
Sunglasses first became polarized in 1936, when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter.
Uses
Hiding one's eyes has implications in face-to-face communication: It can hide weeping, being one of the signs of mourning, makes eye contact impossible which can be intimidating, or can show detachment, which is considered cool in some circles. Darkened sunglasses of particular shapes may be in vogue as a fashion accessory. Note that normal glasses are very rarely worn without a practical purpose — curiously, they can project an image of uncool nerdiness that sunglasses do not have. The impact on nonverbal communication and the cool image are among the reasons for wearing sunglasses by night or indoors. People may also wear sunglasses to hide dilated or contracted pupils or bloodshot eyes (which would reveal drug use), recent physical abuse (such as a black eye), or to compensate for increased photosensitivity. Fashion trends are another reason for wearing sunglasses, particularly designer sunglasses.
People with severe visual impairment, such as the blind, often wear sunglasses in order to avoid making others uncomfortable — not seeing eyes may be better than seeing eyes which seem to look in the wrong direction. Those whose eyes have an abnormal appearance (for example due to cataract) or which jerk uncontrollably (nystagmus) may also do so.
Visual clarity and comfort
Sunglasses can improve visual comfort and visual clarity by protecting the eye from glare.[5] Various types of disposable sunglasses are dispensed to patients after receiving mydriatic eye drops during eye examinations.
Protection
Excessive exposure to ultraviolet radiation (UV) can cause short-term and long-term ocular problems such as photokeratitis, snow blindness, cataracts, pterygium, and various forms of eye cancer.[6] Medical experts often advise the public on the importance of wearing sunglasses to protect the eyes from UV[6]. In the European Union, a CE mark identifies glasses fulfilling quality regulations. In the preparation for solar eclipses, health authorities often warn against looking at the sun through sunglasses alone.
There is no demonstrated correlation between high prices and increased UV protection. A 1995 study reported that "Expensive brands and polarizing sunglasses do not guarantee optimal UVA protection." [7] The Australian Competition and Consumer Commission has also reported that "[c]onsumers cannot rely on price as an indicator of quality".[8] One survey cited below even found a $6.95 pair of generic glasses with slightly better protection than Salvatore Ferragamo shades.[9]
More recently, high-energy visible light (HEV) has been implicated as a cause of age-related macular degeneration[10][11], and some manufacturers design to block it. Sunglasses may be especially important for children, as their ocular lenses are thought to transmit far more HEV light than adults (lenses "yellow" with age).
Some sunglasses also pass ANSI Z87.1 requirements for basic impact and high impact protection. These are voluntary standards, so not all sunglasses comply, nor are manufacturers required to comply. In the basic impact test, a 1 in (2.54 cm) steel ball is dropped on the lens from 50 in (127 cm). In the high velocity test, a 1/4 in (6.35mm) steel ball is shot at the lens at 150 ft/s (45.72 m/s). In both tests, no part of the lens can touch the eye.
Standards
There are three sunglass standards.[12]
The Australian Standard is AS 1067. The five sunglass ratings under this standard are based on the amount of light they absorb, 0 to 4, with “0” providing some protection from UV radiation and sunglare, and “4” a high level of protection.
The US standard is ANSI Z80.3-1972. According to the ANSI Z80.3-2001 standard, the compliable lens should have a UVB (280 to 315nm) transmittance of no more than one per cent and a UVA (315 to 380nm) transmittance of no more than 0.5 times of the visual light transmittance
The European standard is EN 1836:2005. The four ratings are 0 for insufficient UV protection, 1 for sufficient UV protection, 2 for good UV protection and 3 for full UV protection.
(Courtesy of Wikipedia)
