Scientists Say: Photochromic

This word describes chemicals that change shape in response to light


Glasses that change color in the sun are covered in a photochromic pigment — a chemical that changes color in response to light.

Mitja Derenda/istockphoto

Photochromic (adjectve, “Photo-CHROME-ick”)

This word is used to describe a chemical that can change shape in response to a specific wavelength of light. To our eyes, this change in shape changes the chemical’s color.

The lenses of some eyeglasses are coated with a photochromic chemical. When the person wearing the glasses steps outdoors, ultraviolet light from the sun changes the shape of the chemical on the lenses. The chemical then reflects more light and appears darker, changing eyeglasses to sunglasses!  

In a sentence

A teen used a photochromic pigment on her skin to figure out when it was time to reapply her sunscreen.

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Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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