Sunglasses: Encyclopedia II - Sunglasses - Construction

Sunglasses - Construction

Sunglasses - Lens

The color of the lens can vary by style, fashion, and purpose, 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 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 and 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.

Some models have polarized lenses to reduce glare caused by light reflected from polarizing surfaces such as water as well as by polarized diffuse sky radiation (skylight).

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.

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. These type of sunglasses are sometimes called mirrorshades.

The manufacturer, any of the above features: color, polarization, degradation, and mirroring, 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 gradually darken with bright light and lighten in darkness. These are known as photochromic lenses. 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 are typically made from one of four materials. They include glass, plastic (usually acrylic), polycarbonate, and CR-39. Glass lenses have the best optical clarity and scratch resistance, but are heavier than plastic or polycarbonate lenses. They can also shatter or break on impact. Plastic lenses are lighter than glass lenses, but are 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. CR-39 lenses are the most common plastic lenses, due to their low weight, high scratch resistance, low transparency for ultraviolet and infrared radiation, and other advantageous properties.

Sunglasses - Frames

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 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 colored 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 interchangable lenses have a single lens or shield that covers both eyes. Styles that use two lenses also exist, but less common.

Adapted from the Wikipedia article "Construction", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki