Scientists Say Chemistry

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

By Bethany Brookshire

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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Power Words

More About Power Words

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

photochromic     A term used to describe a type of chemical that changes its molecular shape when exposed to light. The change in shape can mean the chemical appears to us to have changed color. 

pigment     A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

ultraviolet     A portion of the light spectrum that is close to violet but invisible to the human eye.

ultraviolet light     A type of electromagnetic radiation with a wavelength from 10 nanometers to 380 nanometers. The wavelengths are shorter than that of visible light but longer than X-rays.

wavelength     The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

About Bethany Brookshire

Bethany Brookshire was a longtime staff writer at Science News Explores. 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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