There are different definitions for categorisation of the spectral range, which are partly determined by applications or special physical phenomena. The basis of non-contact temperature measurement is the measurement of infrared radiation.

For practical use in non-contact temperature measurement, the classification used in the Anglo-American world is relevant:
– near infrared (NIR) is short wavelength IR radiation directly adjacent to the visible (red) range from 0.780µm to 1.4µm.
– short wavelength infrared (SWIR) 1.4µm to 3.0µm.
– mid wavelength infrared (MWIR) with wavelengths from 3.0µm to 8µm.
– long wavelength infrared (LWIR) 8µm to 15µm

In practical applications, pyrometers, infrared temperature sensors and infrared thermometers measure in the following spectral ranges:

Non-metals and coated metals	8µm -14µm
Metal and glass melting	0,8µm – 1,1µm
Graphite, metals, ceramic	1,4µm – 5µm
Glass surfaces	4,8µm – 5,2µm