• Wavelengths of energy outside the visible electromagnetic spectrum at its red-end.
• Use of thermal radiation of wavelengths longer than those of visible light.
• Relating to, producing or employing infrared radiation, to measure temperature.
• Temperature sensors that measure infrared energy
• This measurements technology makes it possible to translate this temperature information into useful infrared pictures.

The electromagnetic spectrum is divided arbitrarily into a number of wavelength re­ gions, called bands, distinguished by the methods used to produce and detect the radiation. There is no fundamental difference between radiations in the different bands of the electromagnetic spectrum. They are all governed by the same laws and the only differences are those due to differences in wavelength.

Thermography makes use of the infrared spectral band. At the short-wavelength end the boundary lies at the limit of visual perception, in the deep red. At the long-wavelength end it merges with the microwave radio wavelengths, in the millimeter range.

The infrared band is often further subdivided into four smaller bands.