Don't be left in the light
Last Updated September 26, 2006
Plutonite or polycarbonate, Ray-Bans or Vuarnets, choosing the right pair of sunglasses can be a nightmare. Here are some tips on what to look for in a pair of sunglasses.
First - What your sunglasses should do for you
- Protect against ultraviolet rays
- Protect from intense light
- Protect from glare
What to look for
Ultraviolet (UV) radiation consists of invisible rays from the sun. Two types reach the earth's surface: ultraviolet-a (UVA) and ultraviolet-b (UVB). Your sunglasses should block both.
UVA rays pass through glass, water, clouds and some clothing. These rays contribute to early wrinkling and cataracts. UVB or the "sun's burning rays," are more dangerous and can cause cancer and photokeratitis (reversible sunburn of the eye).
Keep in mind that the degree of darkness or tint of the lenses will not protect your eyes from UV radiation.
You must buy sunglasses that are UV absorbent, blocking 99 to 100 per cent of all UV light.
Look for the words "blockage" and "absorption" rather than "protection" on the label.
Some manufacturers' labels say UV absorption up to 400nm. This is the same thing as 100 per cent UV absorption.
Sunglasses should be dark enough to reduce the glare but not so dark that they distort colours.
What you plan to use the sunglasses for determines the degree of darkness.
For outdoor sports such as mountain climbing and skiing, you want your shades to block most of the light. These are generally too dark for driving.
General purpose sunglasses block 70 to 90 per cent of light. Cosmetic sunglasses block 60 per cent or less of light and offer only mild UV protection.
Normal frames do not protect your eyes from ambient and direct light and glare from other angles. Wrap-around frames and larger lenses keep the extra light from your eyes.
The tint or colour of the lenses is mostly a matter of personal preference. Grey and brown distort colours the least.
Certain surfaces like water and snow can reflect the light. Sunglasses should eliminate the glare.
Choosing the right type of lens
There are three types of lens material; CR-39, which is plastic made from hard resin; Polycarbonate-synthetic plastic material that is strong and lightweight; and glass which is heavier but more scratch-resistant.
- Regular lenses reduce the brightness of everything evenly.
- Polarizing lenses cut the glare due to reflection, this means they are good for driving and outdoor activities in the snow or on water.
- Photochromic lenses change with the intensity of UV light by turning darker when outdoors and lighter when indoors. If you wear these for driving, choose sunglasses that are fairly dark.
- Mirror lenses reflect all or part of the light instead of absorbing it. They offer no performance advantage as they scratch easily.
One way to test the quality of the lens
Find a surface with repeating lines, hold the sunglasses a short distance from your face and cover one eye. Look through one of the lenses at the lines while moving the sunglasses slowly from left to right and then up and down. The lines should stay straight. If the lines wiggle, the lenses will distort your vision.
Things to keep in mind
- Even if you are wearing 100 per cent UV protection sunglasses, light can still enter from the sides of the glasses and reflect back in your eyes.
- The risk of sun damage is highest between 10 a.m. and 2 p.m.
- If you wear contact lenses that offer UV protection, you still need to wear sunglasses.
- People who spend extended periods of time in the sun without the proper protection can develop photokeratitis. This can cause temporary loss of vision.
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