In addition to four things you should know when selecting sunglasses for cycling or other action sports, there are several aspects of the lenses themselves that will affect their performance and your satisfaction with them. Here's what you should understand about the different features typically available in lenses on sport sunglasses.
1. Lens grade or darkness
Sports sunglasses have a grading scale that measures the lens' ability to screen out visible light.The scale is basically 0 to 5 going from light to dark, where a a grade 0 lens is completely clear and grade 5 is very dark, as in the level of the lens used in welding goggles.
Most cyclists who ride during the day need lens grades between 2 to 3.5. For morning rides it's nice to have low light lenses which start at about grade 0.5.
Because cyclists are exposed to a lot of direct sunlight as well as light reflected from surfaces, you generally need a darker lens. I would go for a medium to dark lens grade between 2 to 3. If you're in very bright environments with no cover, or very little cloud, then you may go for an even darker lens, such as a level 4. I recently went to Australia and in that country due to its very bright and direct sunshine you need a 3.5 to a 4. In the UK and the US a grade 2.5 to a 3 will probably be sufficient.
In the early morning wear a clear lens (grade 0) or a low light lens, such as a grade 0.5 to 1.
Sometimes for convenience a cyclist may turn to a photochromic lens, which automatically adjusts to make itself darker when exposed to UV light. There is a downside with photochromic lenses however, in that they can only adjust up to about 2 grades points.
That means they may not go dark enough in bright sun. So if you buy a nice, lightly tinted base 0.5 photochromic lenses then as it gets brighter, it will only go as dark as 2.5. This may be okay for the UK, but not the Australian outback!
2. Lens Quality
At a minimum, when seeking out cycling sunglasses you should insist on polycarbonate lenses which is the most commonly used impact-resistant lens material available.
And despite what you may hear in the marketing hype from the popular sports sunglasses companies that tries to make their lenses seem different and special, most of the polycarbonate lens materials used by sports sunglasses companies are actually just the same. For example, AMO sunglasses, my company, buys its lenses from the same manufacturer as Rudy Project.
Many sunglasses companies will give you the impression they have a special technology by using clever marketing and unique names for their lens materials. The reality is that the names are really all is that unique, since the lens material largely originates from the same handful of manufacturing companies.
To be sure there are some very good polycarbonate lenses out there, largely as as a result of better quality control of the manufacturing process and more pure raw material. But it is rather difficult to tell run-of-the-mill lenses from truly excellent ones with the naked eye so sticking with a reputable manufacturer is the best way to ensure you are getting the quality and value you seek.
The best quality lenses that are generally available are NXT lenses which do have a proprietary technology based on a different manufacturing process. This is a level up from polycarbonate, and NXT lenses offer superior impact resistance and excellent optical clarity. Additionally, they are flexible and ultra-lightweight (about 10% lighter than polycarbonate) and block 100 percent of UV rays without needing a special coating.
3. Should I go for Optional Extras or Upgrading?
The last bike I bought came with standard components, but I upgraded the gearing and the wheels. It's the same with cycling sunglasses. You get the basic solid features with your desired model and then you can see if there are any "nice to have" upgrades.
For cycling sunglasses these upgrades are typically lens coatings such as a hydrophobic coating, which repels water (useful in a hot climate),or a anti-fog coating useful in a temperate climate or in the cool morning. Where I live it's hot so I go with a hydrophobic coating. The choice is yours and with a good cycling sunglass you can have these options to make your sunglasses perform ideally under the conditions you most commonly encounter. Another upgrade is to an NXT lens as mentioned above.
Polarized lenses can be very comfortable in very bright conditions and will cut reflected glare when sunlight bounces off smooth surfaces like pavement or road.
A nice to have is a photochromic lens which that automatically darkens in bright light and becomes lighter in low light. Great for early morning rides. But beware the limitations of these, in that they might not be able to become as fully dark as you need, depending on where you live and ride.
Though these will cost you more, in the end it is worth it if it allows you to wear your glasses more often, more comfortably.
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Author Tim Hallworth is a triathlete, adventure racer and ultra marathon runner and with his wife is co- founder of AMO sunglasses.
As a special premium for readers of About.com's Bicycling site Tim is offering you an additional 10% discount on the purchase a new pair of AMO sports sunglasses. Just enter discount code "BLOG10" at the AMO Shop.
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