Lens

A range of sunglass models with lenses of different colors, for sale in Manhattan

The color of the lens can vary depending on style, fashion, and purpose, but for general use, red, grey, yellow, 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.
• Orange and yellow lenses increase both contrast and depth perception. They also increase color distortion. Yellow lenses are used bypilots, boaters, fishers, shooters, and hunters for their contrast enhancement and width perception properties.
• Blue or purple lenses are mainly cosmetic.

With the introduction of office computing, ergonomists may recommend mildly tinted glasses for use by display operators, in order to increase contrast.

While some blue blocking sunglasses (see above) are produced as regular sunglasses for exposure to bright sunlight, others—especially formacular degeneration patients—do not block light or other colors in order to function well in regular daylight and even dim sunlight. The latter allow the passage of enough light so normal evening activities can continue, while blocking the light that prevents production of the hormonemelatonin. Low-blue tinted glasses are sometimes recommended to treat insomnia; they are worn in artificial lighting after dark, to reestablish the circadian rhythm.

Some models have polarized lenses, made of Polaroid polarized plastic sheeting, 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, for which 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 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 mirrorshades. A mirror coating does not get hot in sunlight and it prevents scattering of rays in the lens bulk.

Sunglass lenses are made of 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 and shatter-resistant, but are more prone to scratching. 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 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. Gradient 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 (see below). Photochromic lenses gradually darken in bright light.

Frames

Frames are generally made of plastic, nylon, a 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. Oakley, for example, has straight resting hooks on all their glasses, preferring to call them "earstems".

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.

Some sports-optimized sunglasses have interchangeable lens options. Lenses can be easily removed and swapped for a different lens, usually of a different colour. The purpose is to allow the wearer to easily change lenses when light conditions or activities change. The reasons are that 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 has a single lens or shield that covers both eyes. Styles that use two lenses also exist, but are less common.

Nose bridge

This sunglass eyeshield uses a nylon half-frame and interchangeable lenses

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.