Sunglasses (also called sun spectacles – see usage of words for eyepieces) are a kind of visual correction aid, variously termed spectacles or glasses, which feature lenses that are coloured or darkened to screen out strong light from the eyes.

Many people find direct sunlight too bright to be comfortable, especially when reading from paper on which the sun directly shines. In outdoors activities like skiing and flying, the eye can receive more light than usual. It has been recommended to wear these kind of glasses on sunny days to protect the eyes from ultraviolet radiation, which can lead to the development of a cataract. Sunglasses have also been associated with film actors since the lighting involved in production is typically strong and uncomfortable to the naked eye. Also hiding one's eyes has implications in face-to-face communication:

Augusto Pinochet sits with sunglasses in the front of the Chilean Junta

It can hide weeping, being one of the signs of mourning, it can be intimidating as in the stereotype of the guardian of a chain gang, or can show detachedness considered cool in some circles. Also darkened sunglasses of particular shapes can get in vogue as an accessory. Note that, in the Western world, normal glasses are very rarely worn without a practical purpose. Curiously they can project an image of uncool nerdiness that sunglasses don't have. This secondary uses can justify wearing sunglasses by night or indoors.

It is important that the makers of one's sunglasses ensure that the glasses protect against UV (ultraviolet) rays. Lenses that are simply dark but do not provide UV protection may actually make things worse, as the dimmer light causes the pupils to dilate, admitting more UV rays. In the European Union, a CE mark() identifies glasses fulfilling quality regulations. In the preparation for solar eclipses, health authorities often warn against looking to the sun with sunglasses.

The color of the lens can vary with fashion, but for general use, green, grey, or brown is recommended to avoid or minimize color distortion, that could be dangerous when, for instance, driving a car. Grey lenses are considered neutral because do not enhance contrast or distort colors. Brown and green lenses cause some minimal color distortion, but have contrast enhancing properties. Red colored lenses are good for medium and lower light conditions because they are good at enhancing contrast. Orange and yellow lenses have the best contrast enhancement and depth perception. That is why yellow lenses are commonly used by golfers and shooters. Blue and purple lenses offer no real benefits. Clear lenses are used mainly to protect the eyes from impact, debris, or chemicals.

Aside from the lens color, some sunglasses have a mirrored coating on the outer surface. This mirrored coating reflects some of the light when it hits the lens and is useful in bright conditions. These mirrored coatings can be made any color by the manufacturer for styling and fashion purposes.

Other models have polarized lenses to reduce glare.

Some models use a degradation where the top of the glass (through which the sky is looked at) is darker and the bottom is transparent.

Depending on the manufacturer, any of the above features can be combined into a set of lenses for a pair of sunglasses.

With the introduction of office computing , ergonomists can recommend mildly tinted glasses for display operators to increase contrast.

Corrective lenses can be darkened to serve the same purpose, or secondary clip-on dark lenses can be placed in front of the regular lenses. Some lenses made with organic glass gradually darken with bright light and lighten in darkness.

People with severe visual impairment, such as the blind, often wear sunglasses so they do not make others uncomfortable with the fact that they cannot make eye contact with them (not seeing eyes may be better than seeing eyes which seem to look in the wrong direction), or to hide the eyes if their appearance is abnormal, for example due to cataracts. Before the introduction of sunglasses, one-eyed people could wear an eyepatch to not disturb other people. Some people who are severely visually impaired but still sighted wear sunglasses in order to protect their vision against glare.

Lenses typically made from one of three materials. They include glass, plastic (usually acrylic), and polycarbonate. Glass lenses have the best optical clarity and scratch resistance, but are heavier than plastic or polycarbonate lenses. However, they can shatter or break on impact. Plastic lenses are lighter than glass lenses, and more prone to scratching. They do however, offer more resistance to shattering than glass. Polycarbonate lenses are even lighter than plastic lenses. They are shatter-resistant (but not unbreakable) making them good for impact protection.

Frames are generally made from plastic, nylon, or a metal or metal alloy.

History

It is said that the Roman emperor Nero liked to watch gladiator fights through polished gems to recreate with the color and image distortion. Sunglasses were first used in China in the 12th century or possibly earlier. The "lenses" of these glasses were flat panes of smoky quartz, which offered no corrective powers but did protect the eyes from glare, and, according to some sources, evil spirits. Contemporary documents describe the use of such glasses by judges in Chinese courts to conceal their facial expressions while questioning witnesses. Compare the representation of "blind Justice" in Western art.

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.

Sunglasses as such were introduced by Sam Foster in 1929. Foster found a ready market on the beaches of Atlantic City, New Jersey, where he began selling Foster Grants from a Woolworth on the Boardwalk .

Sunglasses would not become polarized, however, until 1936, when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter.

In 2004 Oakley (fashion) has developed Thump, sunglasses with built-in digital audio player.

People predominantly seen wearing sunglasses

Ray Charles

Some celebrities are predominantly seen in public wearing sunglasses. These people include:

• Pedro Abrunhosa
• Alf Arcayan
• Bono
• Habib Bourguiba
• Ray Charles, blind musician
• Tom Clancy
• Elton John, in unusual tints
• Bootsy Collins
• James Dean
• Magenta De Vine
• Andrew Eldritch (of The Sisters of Mercy)
• Gnassingbe Eyadema
• Jose Feliciano, blind musician
• Billy Gibbons (of ZZ Top)
• Heino (German singer)
• Dusty Hill (also of ZZ Top)
• Wojciech Jaruzelski, Polish chief of state
• Theodore Kaczynski, the Unabomber
• Jackie Kennedy, First Lady of the United States
• Karl Lagerfeld, fashion designer
• John Lennon - often wore glasses (corrective or sun-protecting) with distinctive perfectly round lenses.
• Jeff Lynne (of Electric Light Orchestra, possibly as a tribute to Roy Orbison)
• Takashi Miike
• Clayton Moore, The Lone Ranger
• Jack Nicholson
• Yoko Ono, artist and Lennon's wife
• Roy Orbison, singer
• Richard Petty
• Pat Rice (Arsenal football (soccer) coach)
• Julien Roche [[Image:BluesBrothers.jpg|right|thumb|
• Andy Warhol, artist
• Eric Williams
• Stevie Wonder, blind musician
• Mary-Kate Olsen, actress
• Jennifer Black , supermodel

The reasons for this are varied and the behavior is typically the source of much speculation in the yellow press.

Fictional characters predominantly seen wearing sunglasses

Some fictional characters are predominantly depicted as wearing sunglasses. These include:

The Blues Brothers' sunglasses contribute to their distinctive style

• The Blues Brothers, musicians
• The reporter crew of the Argentinian and Spanish shows Caiga Quien Caiga .
• Cliff, the troll "rock" musician in Soul Music
• "Joe Cool", Snoopy's alter-ego
• The Corinthian, from The Sandman (DC Comics Modern Age)
• Crowley, from Good Omens
• Cyclops, from the X-Men - wears sunglasses when he is not in costume with his visor
• Iggy, from Hey Arnold!
• J.C. Denton, from Deus Ex
• The Men in Black and the Men in Black of urban legend.
• The Myst from Starman
• Numbuh One (Nigel), from Codename: Kids Next Door
• Riff from Sluggy Freelance
• Otto, from Rocket Power
• Sparky the Penguin from This Modern World comic strip
• The Terminator
• Most characters from The Matrix movie. Interestingly, all of the protagonists wear rounded lenses, while the antagonists wear rectangular lenses
• Matt Murdoch, blind lawyer from "Daredevil"
• Uncle Duke from Garry Trudeau's comic strip Doonesbury.