Switching Colors with Electricity
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A low jolt of electricity has an unusual effect on certain materials: It changes their color. Such electrochromic materials may change color, darken or go clear in response to the current, and then maintain that change when the power is switched off. A second jolt can completely reverse the change. The reaction occurs due to the chemical process of oxidation and reduction (collectively called redox processes), where electrons are lost or gained, respectively. Redox causes a shift in the bands of the electromagnetic spectrum where the chemical will absorb light, and such shifts in the visible region induce color changes. The effect has been observed since the early 19th century, but Mortimer describes recent experiments to elucidate the cause, as well as how materials are being engineered for practical use. Current commercial devices include car mirrors and plane windows that dim automatically to reduce glare. Proposed applications include multicolor displays, protective eyewear, camouflage materials and chameleonic fabrics.