Infrared Light

Infrared light, within the spectrum of electromagnetic radiation, has a wavelength between 0.7 and 300 micrometers.  It makes up most of the wattage in sunlight, and is invisible to the naked eye. Commonly when discussing infrared, we think of associated applications such as thermal imaging, night vision, and homing devices.

Depending on the particular application of the infrared wavelength, there are various schemes of subdividing the range. The most common scheme is as such:

  • Near-infrared (NIR, IR-A DIN): 0.75-1.4 µm in wavelength, defined by the water absorption, and commonly used in fiber optictelecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles.
  • Short-wavelength infrared (SWIR, IR-B DIN): 1.4-3 µm, water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the dominant spectral region for long-distance telecommunications.
  • Mid-wavelength infrared (MWIR, IR-C DIN) also called intermediate infrared (IIR): 3-8 µm. In guided missile technology the 3-5 µm portion of this band is the atmospheric window in which the homing heads of passive IR ‘heat seeking’ missiles are designed to work, homing on to the IR signature of the target aircraft, typically the jet engine exhaust plume.
  • Long-wavelength infrared (LWIR, IR-C DIN): 8–15 µm. This is the “thermal imaging” region, in which sensors can obtain a completely passive picture of the outside world based on thermal emissions only and requiring no external light or thermal source such as the sun, moon or infrared illuminator. Forward-looking infrared (FLIR) systems use this area of the spectrum. Sometimes also called the “far infrared.”
  • Far infrared (FIR): 15 – 1,000 µm (see also far infrared laser).

Cite: Byrnes, James (2009). Unexploded Ordnance Detection and Mitigation. Springer. pp. 21–22., Wikipedia

Infrared is used in night vision to increase the amount of ambient light intake and present a better image. Although it is not at the core of this technology, it is still a very important element in many night vision devices. Within thermography/thermal imaging, thermographic cameras can read and display the radiation coming from objects. Because the amount of infrared radiation emitted is correspondent to the amount of heat emitted, variations in temperature can be seen. Similarly in homing devices, infrared detectors can be installed since large bodies of heat will release large amounts of infrared radiation. Other applications include spectroscopy (finding the vibration frequency of molecules based on the infrared light produced), meteorology (detecting weather systems using the relation of infrared radiation and heat), and astronomy (detecting celestial bodies using the emission of infrared radiation.)

Various sources: [1], [2], [3], [4]