infra-red, a. [Infra- + red.].
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Lying outside the visible spectrum at its red end; -- said of rays having a longer wavelength (and thus less refrangible) than the extreme red rays, specifically those electromagnetic waves having a wavelength of between 700 nanometers and 1 millimeter. [Webster 1913 Suppl.]
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relating to, using, or producing infrared radiation. [PJC]
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affected by infrared radiation; as, infrared detector; infrared film. [PJC]