Photochromic lenses
Another option to consider are photochromic lenses. These lenses will tint with changes in light intensity. They're a good idea for unpredictable weather when it can be light one minute and dark the next. Mountain bikers benefit from these lenses when swooping between wooded areas and open trails.
With photochromic lenses you don't need to change lenses all the time which can be annoying. However, they don't offer the same range of tint as choosing specific lenses.
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Polarized lenses
Polarized lenses are coated with a special chemical film to reduce glare and reflection so you can see objects ahead with improved clarity. This is especially useful when sun shines on standing water and wet roads. Polarized lenses offer improved UV protection too.
Polarized lenses work by filtering out horizontal light waves which cause glare while leaving vertical light waves (the useful light we use to see clearly).
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Tinted vs polarized lenses
Tinted lenses are very good at reducing brightness and dampening glare. However, polarized lenses will eliminate glare completely without impacting your ability to distinguish shapes and objects ahead of you.
UV protection
Always check cycling glasses for UV protection as the colour of the lens does not accurately represent its ability to block these harmful rays.
Also, be aware that darker lenses without UV protection can cause more eye damage than wearing no sunglasses as your pupil dilates and allows more UV light to enter your eye.
Anti-scratch / shatterproof
A good feature to look for is anti-scratch or shatterproof lenses. Anything from a small stone kicked up by your front wheel to clumsy hands can ruin your lenses, so having this extra protection will reduce expense.
Anti-fog
Anti fog coating or small vents cut into the lens can help to stop your glasses steaming up when you're riding slowly or have stopped at traffic lights.