3. Type of the infrared rays

Infrared Rays are subdivided into several scheme.

ISO 20473 specifies the following scheme:

Designation	Abbreviation	Wavelength
Near-Infrared	NIR	0.78–3 µm
Mid-Infrared	MIR	3–50 µm
Far-Infrared	FIR	50–1000 µm

The International Commission on Illumination (CIE) recommended the division of infrared radiation into the following three bands:

IR-A	0.7 – 1.4 µm, 215 THz – 430 THz
IR-B	1.4  – 3 µm, 100 THz – 215 THz
IR-C	3  – 1000 µm, 300 GHz – 100 THz

Astronomy division scheme

Designation	Abbreviation	Wavelength
Near-Infrared	NIR	0.7–2.5 µm
Mid-Infrared	MIR	2.5–40 µm
Far-Infrared	FIR	40–350 µm.

Sensor response division scheme

Near-infrared	0.7 – 1.0 µm	from the approximate end of the response of the human eye to that of silicon
Short-wave infrared	1.0 – 3 µm	from the cut-off of silicon to that of the MWIR atmospheric window. InGaAs covers to about 1.8 µm; the less sensitive lead salts cover this region.
Mid-wave infrared	3 – 5 µm	defined by the atmospheric window and covered by Indium antimonide [InSb] and HgCdTe and partially by lead selenide [PbSe]
Long-wave infrared	8 – 12, or 7 – 14 µm	this is the atmospheric window covered by HgCdTe and microbolometers
Very-long wave infrared (VLWIR)	12 – 30 µm	covered by doped silicon

Commonly used sub-division scheme

Division Name	Abbreviation	Wavelength	Photon Energy	Characteristics
Near-infrared	NIR, IR-A DIN	0.75–1.4 µm	0.9–1.7 eV	Defined by the water absorption, and commonly used in fiber optic telecommunication 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	0.4–0.9 eV	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; MidIR.[7] Also called intermediate infrared (IIR)	3–8 µm	150–400 meV	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 Infrared signature of the target aircraft, typically the jet engine exhaust plume. This region is known as thermal infrared, but it detects only temperatures somewhat above body temperature.
Long-wavelength infrared	LWIR, IR-C DIN	8–15 µm	80–150 meV	The “thermal imaging” region, in which sensors can obtain a completely passive image of objects only slightly higher in temperature than room temperature, (for example, the human body), based on thermal emissions only and requiring no illumination such as the sun, moon, or infrared illuminator. This region is also called the “thermal infrared.”
Far-infrared	FIR	20–1,000 µm	1.2–80 meV	(see also far-infrared laser and far infrared).