Buyer's guide to sunglass lenses

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Once upon a time, choosing which sunglasses lens to buy was pretty straightforward. But the sheer range and variety of options available today mean taking a long hard look before making that crucial choice.

Sunglass lens technology has come a long way in recent years. New materials are coming onto the market all the time with some significant advances in lens coatings.

Lens coatings provide a protective coating to lenses of all manner of eyewear. Modern polycarbonate lenses, although strong enough for everyday use, can get scratched or they can suffer from wear and tear. A lens coating can increase durability and make sure your sunglasses last longer.

Unfortunately, people don't know a lot about lens coatings are often underplay their advantages.

Lens coatings can be used not alone to improve the life of sunglasses; they can also serve different functions in protecting eyes.

Tints, reflectiveness and photochromic qualities can not only affect the look of sunglasses but also how you see the world.

Blue light, such as the from computer screens, for example, is thought to affect sleep patterns at night so a red tint may help you get some rest.

We've assembled a quick guide to help customers understand more about the world of lens coatings.

Tinted lenses can enhance vision

This is the most straightforward choice, and cosmetics will play a big part in what lens shade you choose. It is merely a case of selecting the colour and the depth of tone that suits you best.

There are some further considerations here. Much depends on the conditions in which you expect to wear sunglasses. OK, bright sunlight is the obvious candidate here, but this is not always the case.

Individual colours can enhance vision in certain conditions, and the choice may not be dependent only on cosmetics. A light blue tint, for example, may look good outdoors but it not okay when glare is a factor, such as when sailing and water is reflected upwards off the surface.

A blue-tinted sunglasses lens can even increase glare in the big outdoors, so choose this tint mainly as a fashion item for streetwear and in the city. For general outdoor holiday wear, brown tinted sunglasses often make the best choice.

Brown filters out the blue glare from water and sky and can also help to increase contrast. Brown coloured lenses are suitable for general outdoor use and brown is a popular choice for standard holiday sunglasses.

Neutral grey tint is a popular choice

Grey is an excellent alternative to brown, retaining decent colour differential and reducing outdoor glare. For this reason, a neutral grey tone is probably the most popular choice, not just for the big outdoors but also for night driving too.

Many also prefer a green-tinted sunglasses lens. Green tint lenses tend to be darker and may be favoured by those with sensitive eyes. Despite blocking out plenty of glare, they can give the highest contrast and the right colour balance.

Yellow and orange tints are the most popular choice for those who are into snow sports such as skiing and snowboarding. Yellow tint sunglasses will soften the harsh white-blue light of pure snow while at the same time, increase colour contrast and depth perception.

Pink and rose-tinted sunglasses can help relieve eyestrain and are more often used by people at computer screens a lot. Colour perception may not be as accurate as other tints.

Many sunglasses carry a graduated tint in any of the above colours. With graduated tones, the colour is strongest at the top of the lens and gets progressively less tinted until it is quite clear.

Graduated tint lenses are suitable for reading, or when carrying out some task that requires clarity when looking downwards but plenty of shade when the eyes are raised.

Photochromic lenses react to light levels

This type of sunglasses lens has a special coating that reacts to sunlight. Often referred to as transition lenses, they become automatically darker as you move into the bright light and lighten when you head out of the sun.

The reaction time of photochromic lenses can vary, but the transition usually gets underway in less than 60 seconds. They continue to get darker, or lighter, for several minutes until reaching the optimum tint for the lighting conditions.

The coating is usually activated by ultraviolet light, which is, in fact, invisible. The darkening and lightening effect happens even on cloudy days and depends only on the amount of UV light that hits the lenses.

Photochromic lenses usually retain a small degree of tint, even in dark conditions. They can be handy for those moving about a lot in varying light conditions such as indoors and outdoors. But they are not much use for driving as headlights pass much too quickly for them to react. Even in daylight, the car windscreen may itself block UV light so the photochromic lenses may be nowhere near as efficient when behind the wheel.

Polarised lenses cut out glare

Popular with drivers and sailors, polarised lenses are particularly useful in eliminating glare from large surfaces such as the sea and sky but with little or no loss of definition. Standard tint lenses reduce light at any angle, while polarised lenses cut out light waves travelling in the horizontal plane and let vertical light waves pass.

Polarisation only reduces glare but also improves both depth and colour perception. Vertically aligned light is much more critical visually than the horizontal rays, the central component of glare.

The glare of the sun on the sea and other flat surfaces can be highly polarised. Likewise, most of the reflected light is horizontal and, with this filtered out by polarised sunglasses images appear more precise.

Polarised sunglasses are especially suitable for driving. The light from bright reflections and the road surface tends to be horizontally polarised. Polarising lenses give higher definition vision for driving, removing the effect of dazzle and reducing eyestrain.

Take care, however, when choosing polarised lenses. Cheap polarised lenses tend to cut out less light, some as little as 10%. High quality polarised lenses will filter out more than 90% of the horizontal rays.