THE SCIENCE & EFFECTIVENESS OF SUNGLASSES
The Science & Effectiveness of Sunglasses
Consumers have an impressive choice when it comes to sunglasses, from rainbow tints to polarized lenses. You can buy very expensive designer sunglasses or cheap ones at a dollar store or drug store. However, you don’t get more UV protection the more money you spend!
The sunglasses at the dollar store with a “UV 400 Protection” sticker on one of the lenses may cost only a couple of dollars and perhaps even feel flimsy, yet they are equally effective in blocking UV rays as a designer pair costing hundreds of dollars.
The Sun is a harsh mistress and while we may enjoy the Sun’s warm infrared rays, its ultraviolet light, invisible and unnoticeable, is more sinister.
Factors Affecting UV Light Exposure and Absorption
The total amount of UV light we are exposed to and absorb is affected by:
- how high we are relative to sea level
- how much time we spend outdoors
- how high the sun is in the sky,
- the amount of pollution in our atmosphere
- whether or not we are taking photosensitizing drugs (medications that increase our absorption of UV rays)
- while UV light can hit our eyes in a straight line, it also gets reflected on the ground and reaches us from below and from the sides.
Harmful Effects of Sun
An impressive number of eye diseases correlate with exposure to UV light, from pre-cancerous growths on the eyelid to snow blindness to conditions affecting the back of the eye. A child’s eye is particularly sensitive to UV exposure. The lens inside their eye is still clear and their pupil is wider. This means that 2 to 5% of the UV rays received by their eyes can actually reach the retina at the back. (By comparison, in adults aged 25 years and older, it’s between 1 and 2%.)
And there’s blue light. Between green-colored light and ultraviolet light, there’s a high-energy region of the visible spectrum that has been implicated in a common form of age-related blindness, though research there is still on-going.
And, of course, exposure to the sun accelerates premature aging of the skin around the eyes.
So we need to protect our eyes from high-energy rays of light. How do we do that?
Casting Light on Sunglasses
UV protection: Glasses advertising “UV 400” will block essentially all UV rays. This is in reference to the wavelength 400 nanometres. And if you’re concerned your sunglasses may not block UV rays after all, you can visit an optician and they’ll use a spectrometer to make the determination. If it goes up to 380 or 390, it’s still very good indeed, but it won’t block 100% of UV light. The UV protection itself does not diminish over time, even though the tint of the lenses could fade.
Price: While you may think that the more expensive a pair of shades is, the better the UV protection is, that is simply not true. A recent study published in the Canadian Journal of Ophthalmology looked at over 200 pairs of sunglasses on sale in Quebec City in three price ranges and tested them to see if they met the standards for filtering out harmful UVs. While there are no mandatory standards in Canada, the researchers used the four existing standards in the world: United States, European Union, Australia, and New Zealand. All tested sunglasses above the 21$ price point met these standards, and almost all of the cheaper sunglasses did as well. Price had clearly no real bearing on their ability to filter out UV light, but it did have a role to play on the clarity of the visible light they transmitted.
If you take a dollar store pair of sunglasses to a major eye-wear chain and ask them to verify its UV protection using their special equipment they will sure enough tell you that they detected 0% of UV rays coming through the lens. So, you may get as much UV protection for only a couple of dollars as a standard designer pair, but the optical quality may lack behind. This means cheap sunglasses can create distortions in shapes, which are annoying and could be hazardous while driving. It’s like looking at the world through an old television set instead of a 4K monitor. So, basically you get what you pay for you.
Tint: The color of the lenses, including how dark they are, has no bearing on the UV protection. It boils down to preference. If you want brighter colors, you go for the brownish, pinkish tint, like the old Serengeti lens. Some people prefer grey lenses, which may lead to a “faded, dim, dark” look without altering colors. As for really dark tints, they simply block more visible light. If your eyes are more sensitive to light, you may want to avoid lighter tints. Orange and yellow lenses offer better contrast, which is useful to tennis players, though they obviously distort colors.
Polarized: While this feature has no impact on UV filtration, it will cut down on glare coming from horizontal surfaces, like snow or the surface of a lake. But if you’re a pilot, watch out! Polarized lenses may interfere with your ability to read instruments that have an anti-glare coating and with LCD readouts, as well as reduce visibility. Hydroplane pilots in particular will have difficulty judging distances for landing while wearing polarized lenses. For everyone else, it’s like having air conditioning in the car. Once you’ve had it, it’s always more comfortable.
Photochromic (AKA transition lenses): The idea of lenses that automatically get darker when go outside is very tempting, but be warned. The technology behind them is triggered by UVB light. Inside a car, where the UVB light is blocked by the windshield, your sunglasses probably won’t darken (although some more recent technology can partly get around that). Also, the transition is not consistent across temperatures. When it’s colder, transition lenses tend to get much darker than when it’s warm.
Wraparound: Because UV light can bounce around, it can reach your eyes from the side. Wraparound sunglasses thus offer better protection.
So we need to protect our eyes from high-energy rays of light. How do we do that?
Casting Light on Sunglasses
UV protection: Glasses advertising “UV 400” will block essentially all UV rays. This is in reference to the wavelength 400 nanometres. And if you’re concerned your sunglasses may not block UV rays after all, you can visit an optician and they’ll use a spectrometer to make the determination. If it goes up to 380 or 390, it’s still very good indeed, but it won’t block 100% of UV light. The UV protection itself does not diminish over time, even though the tint of the lenses could fade.
Price: While you may think that the more expensive a pair of shades is, the better the UV protection is, that is simply not true. A recent study published in the Canadian Journal of Ophthalmology looked at over 200 pairs of sunglasses on sale in Quebec City in three price ranges and tested them to see if they met the standards for filtering out harmful UVs. While there are no mandatory standards in Canada, the researchers used the four existing standards in the world: United States, European Union, Australia, and New Zealand. All tested sunglasses above the 21$ price point met these standards, and almost all of the cheaper sunglasses did as well. Price had clearly no real bearing on their ability to filter out UV light, but it did have a role to play on the clarity of the visible light they transmitted.
If you take a dollar store pair of sunglasses to a major eye-wear chain and ask them to verify its UV protection using their special equipment they will sure enough tell you that they detected 0% of UV rays coming through the lens. So, you may get as much UV protection for only a couple of dollars as a standard designer pair, but the optical quality may lack behind. This means cheap sunglasses can create distortions in shapes, which are annoying and could be hazardous while driving. It’s like looking at the world through an old television set instead of a 4K monitor. So, basically you get what you pay for you.
Tint: The color of the lenses, including how dark they are, has no bearing on the UV protection. It boils down to preference. If you want brighter colors, you go for the brownish, pinkish tint, like the old Serengeti lens. Some people prefer grey lenses, which may lead to a “faded, dim, dark” look without altering colors. As for really dark tints, they simply block more visible light. If your eyes are more sensitive to light, you may want to avoid lighter tints. Orange and yellow lenses offer better contrast, which is useful to tennis players, though they obviously distort colors.
Polarized: While this feature has no impact on UV filtration, it will cut down on glare coming from horizontal surfaces, like snow or the surface of a lake. But if you’re a pilot, watch out! Polarized lenses may interfere with your ability to read instruments that have an anti-glare coating and with LCD readouts, as well as reduce visibility. Hydroplane pilots in particular will have difficulty judging distances for landing while wearing polarized lenses. For everyone else, it’s like having air conditioning in the car. Once you’ve had it, it’s always more comfortable.
Photochromic (AKA transition lenses): The idea of lenses that automatically get darker when go outside is very tempting, but be warned. The technology behind them is triggered by UVB light. Inside a car, where the UVB light is blocked by the windshield, your sunglasses probably won’t darken (although some more recent technology can partly get around that). Also, the transition is not consistent across temperatures. When it’s colder, transition lenses tend to get much darker than when it’s warm.
Wraparound: Because UV light can bounce around, it can reach your eyes from the side. Wraparound sunglasses thus offer better protection.
Anti-reflective (AR) Coating: The standard pair of sunglasses is designed to block 100% of UV rays from entering the front of your lenses. But the reality is sun light is everywhere and enters the eyes from all angles (top, sides and underneath the glasses). In fact, research confirms that 14% to 45% of ambient UV light still reaches the eyes even when traditional sunglasses are worn due to the side and backside exposure. Simply blocking the UV from the front of the lens won’t cut it when it comes to keeping your eyes healthy. To really help protect your eyes, a good pair of sunglasses will reduce the UV rays that reflect off the backside of your lenses by adding an anti-reflective (AR) coating that cut down the reflection of both UV and visible light .When you have this backside UV protection, your eyes – and the skin around your eyes – can be protected up to 98% from UV. Look for premium sun-wear that offers backside AR, like Xperio UV ™ polarized sun lenses.
Summary of Sunglasses
To protect our eyes from the Sun, we should seek out sunglasses that block 99-100% of UVA and UVB rays and we should favor wraparounds. Bigger is better, as the American Academy of Ophthalmology reminds us, but darker is neither better nor worse in this respect. The color does not matter when it comes to blocking harmful rays, and while polarized lenses cut glare, the polarization does not improve the blocking of UV rays.
As for the weather, clouds make no difference: UV light goes through them. And winter is no excuse to leave the shades behind, as the snow reflects 94% of the UV rays it receives. Sunglasses are not just for a sunny day but for every day.
But even with the best shades gracing our faces, we should not forget sunscreen and a hat. While lenses can fully block UV light, wearing sunglasses does not. Light reaches our eyes directly and indirectly, reflected off sidewalks and windows. So, it can enter our eyes from above, below, and from the sides. For this reason, try to wear sunglasses that have anti-reflective coating on the backside of the lenses.
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