How do photochromic glasses work?

Answers (3)

• David Felker

  04/16/2012

  Photochromic lenses are lenses that darken on exposure to ultraviolet (UV) radiation. Once the UV is removed (for example by walking indoors), the lenses will gradually return to their clear state.Photochromic lenses may be made of glass, polycarbonate, or another plastic.Modern photochromic lenses tend to be plastic and instead of silver chemicals they contain organic (carbon-based) molecules that react to light in a slightly different way. Instead of clumping together, they change their color and size when ultraviolet light strikes them.Although each molecule changes by only a fraction of a nanometer, when many molecules respond in the same way the effect can be more dramatic. Imagine lots of molecules suddenly darkening and fattening up inside a clear lens.

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• b3autyqu33nof17

  12/20/2012

  Personally, photochromic glasses is really a wonder thing. They can adjust themselves automatically with the change of UV rays in the air. When you stay in room, the eyeglasses appear clear lenses as regular prescription eyeglasses for vision aids. But when you wear it in sun, the lenses can adjust themselves into black or brown colored lenses(the color of the lenses depend on which color you choose when you buy). It can not only help reduce the strong light, thus give you comfortable vision, but also can prevent UV rays, even glares in the air, therefore to protect your eyes. And all of this miraculous adjustment themselves depends on organic photochromic molecules (for example oxazines and naphthopyrans). So, I think photochromic glasses is worthy to try especially in summer.

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• ESTHER

  04/03/2015

  Modern photochromic lenses tend to be plastic and instead of silver chemicals they contain organic (carbon-based) molecules called naphthopyrans that react to light in a slightly different way: they subtly change their molecular structure when ultraviolet light strikes them. In this altered form, they soak up more ordinary light as it tries to pass by (technically, we say they have a different absorption spectrum), which is what makes the lenses darken. Imagine lots of molecules suddenly darkening inside a clear lens. It's a bit like closing the blinds in front of your window on a sunny day: as the slats turn, they progressively block out more and more light.You might think all of this would take quite a bit of time, but photochromic lenses respond remarkably quickly. About half the darkening happens within the first minute and they're cutting out about 80% of sunlight within 15 minutes.

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