What You Didn't Know About Photochromic Lenses

Photochromic, or light-adaptive, lenses are a type of eyewear lens that automatically adjust their darkness in response to the amount of sunlight or UV (ultraviolet) rays they are exposed to. If you love riding your bike on those moody overcast October days, or enjoy a low-light winter run, these might be your best friend.

photochromic mtb sunglasses

How do photochromic lenses work?

  1. Special Chemicals: Light adaptive lenses contain special photochromic molecules or chemicals that can change their shape when exposed to UV light. These molecules are embedded in the lens material.

  2. UV Light Activation: When you step out into the sunlight, the UV rays from the sun trigger a chemical reaction in the molecules within the lens. This reaction causes the molecules to do a little dance and rearrange themselves.

  3. Darkening Effect: As the molecules do their thing and change shape, they block more and more visible light, which is what makes the lens darker. In turn, this darkening effect reduces the amount of bright sunlight that hits your precious eyeballs.

  4. Light Adaptation: When you go into a shaded area, or the sun decides to set when you're still a good five miles from home, the molecules in the lens return to their original configuration. This makes the lens clear up again, allowing you to see crisp and clear in lower-light conditions.

Some say these are magic lenses that will solve all your variable light issues and help you ride your bike faster than Markus Stöckl. Not sure if that's true, but any lens that automatically and quickly adjusts darkness based on the amount of sunlight has our two enthusiastic thumbs up. 

We've tested many photochromic sunglasses for biking and running and here are our favorites:


Facts About Your Photochromic Sunglasses

  • The process of lightening the lens is typically slower than the darkening process.
  • The speed at which your photochromic lenses darken and lighten depends on a number of factors, including the type of photochromic molecules used, the intensity of the UV light, and the temperature.
  • The darker the lens, the more UV light it absorbs.
  • Photochromic lenses typically darken within a few seconds of being exposed to UV light and lighten within a few minutes of being removed from UV light.

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