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.