- A material which changes color when exposed to light of a given wavelength, and which returns to its original color once the light source is removed. Said especially of light in the visible, near infrared, or near ultraviolet regions. Such a material, for example, may also change from transparent to a given color, and vice-versa when exposed to the appropriate light. Used, for instance, in optical switches, optical filters, optical modulation devices, lenses, optical recording media, charge-coupled devices, and for energy-efficient windows and display panels.
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