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).
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. 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 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 sore eyes from the powerful arc lights 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.
Sunglasses first became polarized in 1936, when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter.
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, like in the stereotype of the guardian of a chain gang as depicted in Cool Hand Luke, 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. Shutter Shades are a prime example of sunglasses worn for fashion rather than functionality due to trends in pop culture.
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.
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.
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. Medical experts often advise the public on the importance of wearing sunglasses to protect the eyes from UV. 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.”  The Australian Competition and Consumer Commission has also reported that “[c]onsumers cannot rely on price as an indicator of quality”. One survey cited below even found a $6.95 pair of generic glasses with slightly better protection than Salvatore Ferragamo shades.
More recently, high-energy visible light (HEV) has been implicated as a cause of age-related macular degeneration, 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.
There are three sunglass standards.
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 providing some protection from UV radiation and sunglare, and 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.
Water sunglasses, also known as surfing sunglasses, surf goggles and water eyewear consist of eyewear specially adapted to be used in turbulent water, such as the surf. Features normally available include
a) shatter proof & impact resistant lenses
b) strap or other fixing to keep glasses in place during sporting activities
c) buoyancy to stop them from sinking should they be displaced from the wearer
d) nose cushion
e) vent or other method to eliminate fogging
Many sports utilize these sunglasses including surfing, windsurfing, kiteboarding, wakeboarding, kayaking, jet skiing, Bodyboarding, and water skiing.
The colour of the lens can vary by style, fashion, and purpose, but for general use, green, grey, yellow, or brown is recommended to avoid or minimize color distortion which would be dangerous when, for instance, driving a car. Gray lenses are considered neutral because they do not enhance contrast or distort colors. Brown and green lenses cause some minimal color distortion, but have contrast-enhancing properties. Red lenses are good for medium and lower light conditions because they are good at enhancing contrast, but cause significant color distortion. Orange and yellow lenses have the best contrast enhancement at depth perception but cause color distortion. Yellow lenses are commonly used by golfers and shooters for its contrast enhancement and depth perception properties. Blue or purple lenses offer no real benefits and are mainly cosmetic. With the introduction of office computing, ergonomists can recommend mildly tinted glasses for display operators to increase contrast. Clear lenses are used typically to protect the eyes from impact, debris, dust, or chemicals. Some sunglasses with interchangeable lens have optional clear lenses to protect the eyes during low light or night time activities. Debates exist as to whether “blue blocking” or amber tinted lenses may have a protective effect. Blue blocking sunglasses typically also block some light of other colors to function well in full sunlight. Some low blue glasses are for use inside at night to avoid suppression of the sleep promoting hormone melatonin. They provide enough light so normal evening activities can continue.
Some models have polarized lenses, made of Polaroid polarized plastic sheet, to reduce glare caused by light reflected from polarizing surfaces such as water (see Brewster’s angle for how this works) as well as by polarized diffuse sky radiation (skylight). This can be especially useful when fishing, as the ability to see beneath the surface of the water is crucial.
A mirrored coating can also be applied to the lens. This mirrored coating reflects some of the light when it hits the lens before it is transmitted through the lens making it useful in bright conditions. These mirrored coatings can be made any color by the manufacturer for styling and fashion purposes. The color of the mirrored surface is irrelevant to the color of the lens. For example, a gray lens can have a blue mirror coating, and a brown lens can have a silver coating. Sunglasses of this type are sometimes called mirrorshades. A mirror does not get hot in the sunlight and prevents scattering in the lens bulk.
Sunglass lenses are made from either glass or plastic. Plastic lenses are typically made from acrylic, polycarbonate, CR-39 or Polyurethane. Glass lenses have the best optical clarity and scratch resistance, but are heavier than plastic lenses. They can also shatter or break on impact. Plastic lenses are lighter but are more prone to scratching. Plastic offers more resistance to shattering than glass. Polycarbonate plastic lenses are the lightest, and are also almost shatterproof, making them good for impact protection. CR-39 is the most common plastic lens, due to their low weight, high scratch resistance, and low transparency for ultraviolet and infrared radiation.
Any of the above features: color, polarization, gradation, mirroring, and materials can be combined into the lens for a pair of sunglasses. Gradated glasses are darker at the top of the lens where the sky is viewed and transparent at the bottom. Corrective lenses or glasses can be manufactured with either tinting or darkened to serve as sunglasses. An alternative is to use the corrective glasses with a secondary lenses such as oversize sunglasses that fit over the regular glasses, clip-on lens that are placed in front of the glasses, and flip-up glasses which feature a dark lens that can be flipped up when not in use. Photochromic lens gradually darken in bright light.
Frames are generally made from plastic, nylon, a metal or metal alloy. Nylon frames are usually used in sports because they are light weight and flexible. They are able to bend slightly and return to their original shape instead of breaking when pressure is applied to them. This flex can also help the glasses grip better on the wearer’s face. Metal frames are usually more rigid than nylon frames thus they can be more easily damaged when participating in sporty activities, but this is not to say that they cannot be used for such activities. Because metal frames are more rigid, some models have spring loaded hinges to help them grip the wearer’s face better. The end of the ear pieces and the bridge over the nose can be textured or have a rubber or plastic material to hold better. The end of the ear pieces are usually curved so that they wrap around the ear; however, some models have straight ear pieces. Oakley, for example, has straight ear pieces on all their glasses.
Frames can be made to hold the lenses in several different ways. There are three common styles: full frame, half frame, and frameless. Full frame glasses have the frame go all around the lenses. Half frames go around only half the lens, typically the frames attach to the top of the lenses and on the side near the top. Frameless glasses have no frame around the lenses and the ear stems are attached directly to the lenses. There are two styles of frameless glasses: those that have a piece of frame material connecting the two lenses together, and those that are a single lens with ear stems on each side.
Some sports-oriented sunglasses have interchangeable lens options. Lenses can be easily removed and swapped with a different lens, usually a different coloured lens. The purpose of this is to allow the wearer to easily change lenses when light conditions or activities change. The reason for this is because the cost of a set of lenses is less than the cost of a separate pair of glasses and carrying extra lenses is less bulky than carrying multiple pairs of glasses. It also allows easy replacement of a set of lenses if they are damaged. The most common type of sunglasses with interchangeable lenses have a single lens or shield that covers both eyes. Styles that use two lenses also exist, but are less common.
Nose bridges allow support between the lens and the face. Nose bridges also prevent pressure marks caused by the weight of the lens or frame on the cheeks. People with large noses may need a low nose bridge on their sunglasses. People with medium noses may need a low or medium nose bridge. People with small noses may need sunglasses with high nose bridges to allow clearance.