HOW SUNGLASSES WORK

Besides being a fashion accessory, sunglasses provide necessary health benefits. A high-quality pair of sunglasses can provide protection from harmful ultraviolet (UV) rays, protect your irises from overexposure to intense light and glare, and block out certain frequencies of light. But how do these accessories manage to protect your eyes from the sun?

A pair of sunglasses seems so simple – two pieces of tinted glass or plastic in some sort of frame. How much more straightforward can it be? But a variety of technologies is used to eliminate the problems we encounter with different kinds of light. Buying the right pair of good sunglasses for the conditions in which you use them gives you maximum protection and performance.

There are three different categories of light that we see: direct, reflected, and ambient. Direct light is light that comes directly from the source to your eyes, for example the sun or a street light (although it is not a good idea to look directly into these!) Reflected light, typically called glare, is light that has bounced off a reflective surface, such as water or sand, and can be harsh on the eyes. Ambient light is light that has no clear source, for example the glow that surrounds a city at night.

Sunglass Technology

The most obvious technology to shield our eyes against harmful light is tinting.Different tints are used to achieve different results. Grey tints are all-purpose tints that reduce the overall brightness with the least amount of colour distortion, and offer good protection against glare. A yellow tint virtually eliminates the blue part of the colour spectrum, making everything bright and sharp, but it does distort colour perception. Amber or brownish tints are also good all-purpose tints; they distort colour to some extent but increase contrast and clarity. Green tints are the most popular because they offer the highest contrast and greatest visual acuity. Purple or rose tints offer the best acuity of objects against a blue or green background.

Most of the glare that causes you to wear sunglasses comes from horizontal surfaces, such as water or a highway. Polarised lenses in sunglasses are fixed at an angle that allows vertically polarised light through, significantly reducing the glare. A lot of sunglasses advertised as polarising actually are not, so be sure that you are buying polarising glasses.

Photochromic lenses are lenses which darken when exposed to the sun, and lighten when you go indoors away from UV light, making them useful if you are wearing prescription glasses and you don’t want to keep changing from clear glasses to sunglasses.

A common problem with sunglasses is light reflecting off the back of the lenses into the eyes. Anti-reflective coating helps to reduce this back-glare. Anti-reflective coating is also often applied to prescription glasses and sunglasses to reduce the glare that reflects off the lenses.

Several of the most serious eye problems, such as cataracts, can be linked to ultra-violet (UV) light. A good ultra-violet coating on your sunglasses can eliminate UV radiation, and should filter out 100% of both A and B UV rays. For people with very sensitive eyes, some sunglasses offer protection from infrared as well as UV radiation.

Reflective sunglasses often have a mirrored look, and reflect about half the light that strikes the lenses, while allowing the other half through. Often, the coating is applied as a gradient shaded from top to bottom, which provides additional protection from light coming from above, while allowing more light in from below or straight ahead.

While glass is naturally scratch-resistant, most plastic is not, so a scratch-resistant coating is often applied to plastic lenses.

Choosing the Perfect Sunglasses

The key to finding the perfect pair of sunglasses is to pick the right features for your situation. Some of the most important features to consider include:

Lens material - Polycarbonate is a synthetic plastic material that has great strength and is very lightweight. Glass lenses are heavier but are much more resistant to scratches.

Lens quality - Optical-quality polycarbonate and glass lenses are free of distortions, such as blemishes or waves, and have evenly distributed colour across each lens.

Lens darkness - What you plan to use the sunglasses for determines the darkness of the tint. For outdoor sports, choose a tint that blocks more light, while for driving a tint that blocks less light is suitable. Tints that offer minimal light blockage are mainly good for fashion since they offer only mild protection.

Special coatings or features - Anti-reflective, waterproof, mirror and scratch-resistant coatings improve the functionality of the sunglasses but also add cost. Many of the more expensive sunglasses use specific technologies including polarisation, tinting and anti-reflective coatings to achieve increased clarity, better protection, higher contrast or to block certain types of light.

Frame and lens design - Normal frames similar to prescription eyeglass frames filter the light coming through the lenses but offer no protection from ambient light, direct light and glare from other angles. Wrap-around frames and larger lenses can keep this extra light from your eyes.

Frame material - The material used to make the frames is often a huge factor in cost and durability.

Brand recognition - The simple truth is that a brand name does add cost. However, it is possible to find high-quality sunglasses that don't have a brand-name price.

So the next time you’re shopping for a new pair of shades, look closely at the label to see what protection it offers. Now that you’re aware of the importance of eye protection, you have no excuse to forgo function for fashion. Buying the right pair of good quality sunglasses for the conditions in which you wear them gives you maximum protection and performance.