Infrared light

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In physics, infrared (IR) light refers to a non-visible portion of the electromagnetic spectrum ranging from wavelengths of 750 nm to 1 mm. The name infrared comes from Latin infra- meaning below, i.e., infrared has a lower frequency than red in the spectrum.

Various disciplines further subdivide the IR, but there is no consensus on the divisions. They vary from discipline-to-discipline and even widely within a given discipline. The following table shows a typical set of divisions:

Name Acronym Range
Near Infrared NIR 0.7 - 1.4 microns
Short-Wave Infrared SWIR 1.4 - 3.0 microns
Mid-Wave Infrared MWIR 3.0 - 5.0 microns
Long-Wave Infrared LWIR 5.0 - 20.0 microns

Forward-looking infrared viewing systems work in the LWIR, and, recently, MWIR. Night vision devices often are sensitive into the NIR.