Choosing the best sunglasses

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OK, so you want a new pair of sunglasses and you really like to look cool. But there is more to it choosing sunglasses just because they are the latest craze. There are lots of other factors to consider when picking a pair of sunglasses.

Protection from the sun is a given in choosing sunglasses but few people really understand the effects of harmful ultraviolet (UV) rays, the different effects of sunglass tints and the real reason why some sunglasses are so very cheap and others are really expensive.

Other things to consider in choosing a pair of sunglasses vary from the personal — your face shape, skin complexion and so on — to the practical, like image clarity, robustness, weight and cost.

The most important factor to consider in buying sunglasses is the lens. These can be composed of glass, polyurethane, polycarbonate or acrylic. Each has its advantages and drawbacks.

Glass has the best optical clarity and is less likely to get scratches, but it is heavier and pricier than alternatives and is less resistance to impact.

Polyurethane will also give high clarity and good impact resistance and it's light and flexible, but it is also the most expensive, especially if it has extra coated layers.

Polycarbonate also scores well on impact resistance, is light, flexible and cheap, but it does scratch more easily and does not have the clarity of glass or polyurethane.

Acrylic is cheaper but scores less well on all the other points. It is much less durable and the sunglasses may have some image distortion.

Whatever type of lens you choose it will certainly come with some type of colour tinting and each type has its strength. All sunglass lens tints reduce overall brightness and protect the eyes from the glare but they will differ in colour, contrast and depth of field vision.

Colour neutral tints such as grey and green lenses filter out light right across the spectrum and will help to reduce eyestrain. Yellow and amber lenses are best in low-level white light and offer good depth perception, ideal for a skiing holiday for example. Drivers should choose red or rose-tinted sunglasses as these work best in low light conditions, offering good a depth of field.

Mirror lenses may look stylish, but they mainly reduce glare by reflecting much of the light away from the eye so clarity is reduced and images will appear much darker than they actually are.

It is a good idea to have different sunglasses for different seasons of the year. In the summer when the sun is brightest, a darker shade will reduce glare whilst in the winter lighter lens shades will improve visibility in low levels of sunlight.

Sunglasses can come with several layers of coating and, the more expensive they are the higher the number of coatings they are likely to have. Coatings on sunglasses can help to repel water, reduce scratching and prevent misting.

Lenses are usually made using one of two methods. Injection offers greater optical clarity, but it comes at a price. Cheaper lenses are bent into shape and come with a range of options with expensive high-end sunglasses using a longer process to achieve higher optical clarity.

Polaroid lenses are great for those who don't like glare or if you enjoy water sports. Special filters in polarized sunglass lenses block out horizontal light waves but let vertical waves through substantially reducing glare without loss of clarity, especially off large flat surfaces such as a lakes or seas.

Again, you get what you pay for. Cheaper sunglasses have a polarizing filter applied as an external film coating while more expensive models sandwich the polarizing layer inside the lens with adhesive. The latest technology allows the polarizing filter to be bonded with the lens while it is still liquid form with no need for adhesives that can affect the optical quality.

Ultraviolet (UV) rays from the sun can damage your eyes and long-term exposure is linked to eye disease, so protection must be high on anyone's list in choosing sunglasses. There are three types of UK ray to consider. UVb rays are the ones to be avoided. UVa rays are absorbed by the eye and pose little threat while UVc are filtered out by the atmosphere.

The tip here is always to look at the label. UV protection information should be printed on the tag or sticker and if it is missing, put them back on the rack. Beware too of heavily tinted sunglasses with limited UV protection and they can do more harm than good. Your own eye lens will open wider to compensate for the tint and expose it to more UV rays.