THE USE OF SUNGLASSES
People may also wear sunglasses to hide an abnormal appearance of their eyes. This can be true for people with severe visual impairment, such as the blind, who may wear sunglasses to avoid making others uncomfortable. The assumption is that it may be more comfortable for another person not to see the hidden eyes rather than see abnormal eyes or eyes which seem to look in the wrong direction. People may also wear sunglasses to hide dilated or contracted pupils, bloodshot eyes due to drug use, recent physical abuse, bulging eyes, a cataract, or eyes which jerk uncontrollably.
The European standard EN 1836:2005 has four transmittance ratings: “0” for insufficient UV protection, “2” for sufficient UHV protection, “6” for good UHV protection and “7” for “full” UHVV protection, meaning that no more than 5% of the 380 nm rays are transmitted. Products which fulfill the standard receive a CE mark. There is no rating for transmittance protection for radiation of up to 400 nm, as required in other countries (incl. the United States) and recommended by experts. The current standard EN 1836:2005 was preceded by the older standards EN 166:1995 (Personal eye protection –Specifications), EN167: 1995 (Personal eye protection – Optical test methods), and EN168: 1995 (Personal eye protection – Non-optical test methods), which in 2002 were republished as a revised standard under the name of EN 1836:1997 (which included two amendments). In addition to filtering, the standard also lists requirements for minimum robustness, labeling, materials (non-toxic for skin contact and not combustible) and lack of protrusions (to avoid harm when wearing them).
Sunglasses sold in the United States are regulated by the Food and Drug Administration and are required to conform to safety standards. The U.S. standard is ANSI Z80.3-2001, which includes three transmittance categories. According to the ANSI Z80.3-2001 standard, the lens should have a UVB transmittance of no more than one per cent and a UVA transmittance of no more than 0.3 times the visual light transmittance. The ANSI Z87.1-2003 standard includes requirements for basic impact and high impact protection. In the basic impact test, a 1 in steel ball is dropped on the lens from a height of 50 in. In the high velocity test, a 1/4 in steel ball is shot at the lens at 150 ft/s. To pass both tests, no part of the lens may touch the eye.
When driving a vehicle, particularly at high speed, dazzling glare caused by a low sun, or by lights reflecting off snow, puddles, other vehicles, or even the front of the vehicle, can be lethal. Sunglasses can protect against glare when driving. Two criteria must be met: vision must be clear, and the glasses must let sufficient light to get to the eyes for the driving conditions. General-purpose sunglasses may be too dark, or otherwise unsuitable for driving.
Graduated lenses, with the bottom part lighter than the top, can make it easier to see the controls within the car. All sunglasses should be marked as meeting the standard for the region where sold. An anti-reflective coating is recommended, and a hard coating to protect the lenses from scratches. Sunglasses with deep side arms can block side, or peripheral, vision and are not recommended for driving. Even though, some of these glasses are proven good enough for driving at night, it is strongly recommended not to do so, due to the changes in a wide variety of light intensities, especially, while using yellow tinted protection glasses. The main purpose of these glasses, are to protect the wearer from dust and smog particles entering into the eyes while driving at high speeds.
Many of the criteria for sunglasses worn when piloting an aircraft are similar to those for land vehicles. Protection against UV radiation is more important, as its intensity increases with altitude. Polarized glasses are undesirable as aircraft windscreens are often polarized, intentionally or unintentionally, showing Moire patterns on looking through the windscreen; and some LCD displays used by instruments emit polarized light, and can dim or disappear when the pilot turns to look at them as do corrective glasses, sunglasses have to meet special requirements when worn for sports. They need shatterproof and impact-resistant lenses; a strap or other fixing is typically used to keep glasses in place during sporting activities, and they have a nose cushion.
Special protection is required for space travel because the sunlight is far more intense and harmful than on Earth, where it is always filtered through the atmosphere. Sun protection is needed against much higher UV radiation and even against harmful infrared radiation, both within and outside the spacecraft. Within the spacecraft, astronauts wear sunglasses with darker lenses and a thin protective gold coating. During space walks, the visor of the astronauts’ helmets, which also has a thin gold coating for extra protection, functions as strong sunglasses. The frames of sunglasses and corrective glasses used in space must meet special requirements. They must be flexible and durable, and must fit firmly in zero-gravity. Reliable fit is particularly important when wearing corrective glasses underneath tight helmets and in space suits: once inside the spacesuit, slipped glasses cannot be touched to push them back into place, sometimes for up to ten hours. Frames and glasses must be designed so that small pieces of the glasses such as screws and glass particles cannot become dislodged, then float and be inhaled. 90% of astronauts wear glasses in space, even if they do not require corrective glasses on Earth, because zero-gravity and pressure changes temporarily affect their vision.
The first sunglasses used in a Moon landing were the original pilot sunglasses produced by American Optical. In 1969 they were used aboard the Eagle, the lunar landing module of Apollo 11, the first manned mission to land on the Moon. NASA research primarily by scientists James B. Stephens and Charles G. Miller at the JET Propulsion Laboratory resulted in special lenses that protected against the light in space and during laser and welding work. The lenses used colored dyes and small particles of zinc oxide, which absorbs ultraviolet light and is also used in sunscreen lotions. The research was later broadened to further terrestrial applications, e.g., deserts, mountains, and fluorescent-lighted offices, and the technology was commercially marketed by a U.S. company. Since 2002 NASA used the frame of the designer model Titan Minimal Art of the Austrian company Silhouette, combined with especially dark lenses developed jointly by the company and NASA optometrist Keith Manuel. The frame is very light at 1.8 grams, and does not have screws or hinges that could detach.
The color of the lens can vary depending on style, fashion, and purpose, but for general use, red, grey, green, or brown are recommended to avoid or minimize color distortion, which could affect safety when, for instance, driving a car or a school bus. Gray and green lenses are considered neutral because they maintain true colors. Brown lenses cause some color distortion, but also increase contrast. Turquoise lenses are good for medium and high light conditions, because they are good at enhancing contrast, but do not cause significant color distortion. Yellow is “optimum for object definition, but creates a harsh visible light”; amber “allegedly makes distant objects appear more distinct, especially in snow or haze. These lenses are popular with skiers, hunters, boaters and pilots.” Blue or purple lenses are mainly cosmetic.
A mirrored coating can be applied to the lens. This mirrored coating deflects some of the light when it hits the lens so that it is not transmitted through the lens, making it useful in bright conditions; however, it does not necessarily reflect UV radiation as well. 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 mirror shades. A mirror coating does not get hot in sunlight and it prevents scattering of rays in the lens bulk.
Frames are generally made of plastic, nylon, metal, or a metal alloy. Nylon frames are usually used in sports because they are lightweight 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 the wearer participates in sport 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 resting hook and the bridge over the nose can be textured or have rubber or plastic material to improve hold. The ends of the resting hook are usually curved so that they wrap around the ear; however, some models have straight resting hooks. 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, and those that are a single lens with ear stems on each side. Nose bridges provide support between the lens and the face. They 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.
Gradient lenses go from a darker shade at the top to a lighter one at the bottom, so there will be more protection from sunlight the higher one looks through the lens, but the lower one looks through the lens, the less protection is offered. An advantage is that one can wear them indoors without fear of tripping over something and also allowing the user to see. Wearing sunglasses to nightclubs has become common in recent times, where the gradient lens comes in handy. Gradient lenses may also be advantageous for activities such as flying airplanes and driving automobiles, as they allow the operator a clear view of the instrument panel, low in his line of sight and usually hidden in shadow, while still reducing glare from the view out the windscreen.
Mirrored lenses, having a metallic, partially reflective coating on the outer surface, combined with a tinted glass lens, are an alternative to polarization for UV protection, improving contrast when depth perception is important such as seeing moguls and ice while skiing or snowboarding. The mirrored lens reflects glare to protect the eyes, but improves the ability to see contrasts, and mirrored lenses of different colors can expand the range of fashion styles.
In the early twenty-first century moderately oversized sunglasses have become a fashion trend. There are many variations, such as the “Onassis”, discussed below, and Dior white sunglasses. Onassis glasses or “Jackie O’s” are very large sunglasses worn by women. This style of sunglasses is said to mimic the kind most famously worn by Jacqueline Kennedy Onassis in the 1960s. The glasses continue to be popular with women, and celebrities may use them, ostensibly to hide from paparazzi.
Oversized sunglasses, because of their larger frames and lenses, are useful for individuals who are trying to minimize the apparent size or arch of their nose. Oversized sunglasses also offer more protection from sunburn due to the larger areas of skin they cover, although sunblock should still be used.
“Tea-shades” (sometimes also called “John Lennon glasses”, “Round Metal”, or, occasionally, “Granny Glasses”) were a type of psychedelic art wire-rim sunglasses that were often worn, usually for purely aesthetic reasons, by members of the 1960s counterculture. The original tea-shade design was made up of medium-sized, perfectly round lenses, supported by pads on the bridge of the nose and a thin wire frame. When tea-shades became popular in the late 1960s, they were often elaborated: Lenses were elaborately colored, mirrored, and produced in excessively large sizes, and with the wire earpieces exaggerated. A uniquely colored or darkened glass lens was usually preferred. Modern versions tend to have plastic lenses, as do many other sunglasses. Tea-shades are hard to find in shops today; however, they can still be found at many costume Web sites and in some countries.
The Ray-Ban Wayfarer is a plastic-framed design for sunglasses produced by the Ray-Ban company. Introduced in 1952, the trapezoidal lenses are wider at the top than the bottom and were famously worn by James Dean, Roy Orbison, and other actors and singers. The original frames were black; frames in many different colors were later introduced. There is always a silver piece on the corners as well.
Wrap-around (sometimes also called “Yoko Ono glasses”) is a style of sunglasses characterized by being strongly curved, to wrap around the face. They may have a single curved semi-circular lens that covers both eyes and much of the same area of the face covered by protective goggles, usually with a minimal plastic frame and single piece of plastic serving as a nosepiece. Glasses described as wraparound may alternatively have two lenses, but again with a strongly curved frame.