infrared (IR) radiation Electromagnetic waves beyond red end of visible spectrum, with range of wavelength 0.7 m m to 1mm. Infrared radiation is emitted by all the surfaces at all temperatures below 6000 K. The molecular vibrations and rotations produce IR radiation. The night vision devices are infrared detectors. The optical parts of such devices are made of quartz, germanium or some varieties of polyethylene which are transparent to IR radiation.