Portion of the electromagnetic spectrum that extends from the microwave range to the red end of the visible light range. Its wavelengths vary from about 0.7 to 1,000 micrometres. Most of the radiation emitted by a moderately heated surface is infrared, and it forms a continuous spectrum. Molecular excitation produces extensive infrared radiation but in a discrete spectrum of lines or bands. Infrared wavelengths are useful for night-vision equipment, heat-seeking missiles, molecular spectroscopy, and infrared astronomy, among other things. The trapping of infrared radiation by atmospheric gases is also the basis of the greenhouse effect.
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