| discovery center How Photochromic Eyeglass Lenses Work The result of years of research and development, today's photochromic lenses are the product of highly sophisticated technologies. 
In its most basic form, a photochromic lens changes color because of a chemical reaction. When someone wears photochromic lenses outside, exposure to UV causes the lenses to darken. Indoors, at night, or on cloudy days there isn't as much UV to cause the chemical reaction. Therefore, the lenses remain relatively clear. return to top
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