SUNGLASSES

Sunglasses 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.
Many people find direct sunlight too bright to be comfortable, especially when reading from paper in direct sunlight. In outdoor activities like riding, skiing and flying, the eye can receive more light than usual. It has been recommended to wear these kind of glasses whenever outside to protect the eyes from ultraviolet radiation, which can lead to the development of a cataract. Sunglasses have also been associated with celebrities and film actors primarily due to the desire to mask identity, but in part due to the lighting involved in production typically being stronger than natural light and uncomfortable to the naked eye. Since the 1950s sunglasses have been popular as a fashion statement, especially on the beach.

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, or to compensate for increased photosensitivity. Fashion trends are another reason for wearing sunglasses, particularaly 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.

Excessive exposure to ultraviolet radiation (UV) can cause short-term and long-term ocular problems such as photokeratitis, snow blindness, cataracts, pterygium, and various eye cancers. 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 unscientific survey 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 “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.

Lens
The color 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 causes 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 and purple lenses offer no real benefits and are mainly cosmetic. 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.