What makes sunglasses work

As our understanding of the damaging nature of sunlight evolved, the need for better eye protection was recognized, and technology was developed to help sunglasses better screen out the harmful rays of the sun, especially UV rays.

From inexpensive models with plastic lens and frames to costly designer brands with ground glass lenses and custom-made frames, sunglasses are available in a staggering array of styles and prices.

Unfortunately there is no way to tell from the color or darkness of the lens how well it will screen out UV light. Similarly, there is little relationship between price of glasses and their ability to block UV light. Sunglasses consist of a pair of light-filtering lenses and a frame to hold them in place.

The vast majority of lenses are made of colorized plastic, such as polycarbonate. However, glass is still employed for high quality brands. The highest quality lenses are optically accurate and do not distort shapes and lines.

These lenses, like camera lenses, are made from distortion-free ground and polished optical glass. The borosilicate glass used in these lenses is scratch resistant and is made impact resistant by tempering it with various chemical treatments. Soluble organic dyes and metallic oxide pigments are added to the lens material to absorb or reflect light of certain frequencies.

These additives must not distort colors excessively, however; for example, badly colored lenses may make it difficult to discern the correct color of traffic lights. Gray lenses produce the least distortion for most people, although amber and brown are good too. Blue and purple tend to distort too much color. The additives also should block at least part of the blue light which is part of the lower frequency UV rays.

Brown or amber screen out blue light the best, but at the cost of some color distortion. Various chemical coatings which are added to the lens can enhance viewing by reducing reflection or screening out polarized light. Sunglass frames are made from metal or plastic.

Metal frames, particularly expensive ones, are often made of mixtures of nickel and other metals such as silver. These frames have precisely engineered features, such as sculpted and gimbaled nose-pads, durable hinges with self-locking screws, and flexible temples.

Upscale manufacturers use combinations of nickel, silver, stainless steel, graphite, and nylon in their leading-edge designs.

There are two key elements to consider regarding sunglasses design, fashion and function. In the last few decades sunglasses have become a high fashion item, and the current design process reflects this status. Upscale clothing designers, fragrance marketers, and sporting goods vendors custom-design sunglasses to promote their own specific image. By and large these design changes are not functional; they are intended to increase the fashion appeal of the glasses.

Stylized frames, uniquely shaped lenses, and embossed logos are all part of this designer mystique. While some designs are considered "classic" and timeless, others must be continually updated to satisfy the public's constantly changing tastes. The children's sunglasses market is another area which requires frequent redesign, since the style of the glasses changes from season to season based on merchandising tie-ins with popular cartoon or other characters.

From a functional standpoint, sunglasses are designed specifically for a variety of outdoor activities. Sports enthusiasts have specific requirements that are reflected in sunglass design. For example, sunglasses designed for trap shooters are designed to provide maximum contrast to allow better viewing of their clay pigeon targets.

On the other hand, sunglasses for skiers are designed to counter the light reflected of snow-covered surfaces. Lenses of the this types are known as blue blockers, because they filter out violet, blue, and some UV rays. Fisherman and boaters have their own special needs that must be addressed as well.

Polarization has nothing to do with UV light absorption, but many polarized lenses are now combined with a UV-blocking substance. Check the label to make sure the lenses provide maximum UV protection. The same goes for lens color and tint, lens darkness, and mirror coating. If you spend a lot of time outdoors, especially around water, consider wrap-around sunglasses that protect from UV rays that come in from the side.

This design will also stop the wind that makes your eyes dry. They can also make it easier to see objects below the surface of a lake or stream. The optometric lab can easily add polarization to the lens during the fabrication process.

Note that polarized sunglasses can interfere with viewing LCD screens like those on many car instrument panels and smartphones. They are also not recommended when you are navigating on icy roads. Sunglass lenses frequently contain one or more special-purpose coatings.

UV coating — Glass and plastic lenses often contain a UV coating. Anti-reflective coating — This coating is affixed to the backside of the sunglass lenses. Scratch-resistant coating — A scratch-resistant coating aims to prevent scratches from damaging delicate sunglass lenses. This coating is applied to both sides of the lenses and is especially important for lightweight and easily scratched materials such as polycarbonate and high-index plastic. The color of the lenses is one of the primary characteristics of sunglasses.

Other than just liking the way you look in red or blue or orange lenses, why should you choose one color over another? Here are the most common lens colors and why you might pick one over another. Gray — The most neutral tint. It affects your color vision the least. Great for most activities. Green — Provides contrast and helps reduce glare and eye strain. Ideal for golf, tennis and everyday use. Red or rose — Block blue light, so they improve driving visibility while reducing eye strain.

They enhance detail and increase depth of field. They work well for hunting, cycling and snow and water sports. Blue or purple — Deliver enhanced color perception. They compliment most skin tones and work well in foggy weather. Amber or brown — Increase contrast and heighten visual acuity. Perfect for most sports since they improve contrast against green grass and blue skies. Yellow, orange or gold — Improve visibility of objects, particularly in moderate- to low-light conditions.

Excellent for both indoor and outdoor activities. Mirrored lenses have a very thin coating that reflects light. Silvered aviator sunglasses are the classic example.