Blackbody radiation law: Blackbody is an idealized radiation body that absorbs radiation energy of all wavelengths without any reflection or transmission of energy. Its surface emissivity is 1, and the reflection coefficient of other substances is less than 1, which is called gray body. It should be pointed out that there is no real blackbody in nature, but in order to understand and obtain the distribution law of infrared radiation, it is necessary to choose a suitable model in theoretical research. This is the quantum oscillator model of body cavity radiation proposed by Planck, which derives the law of Planck blackbody radiation, that is, the spectral radiance of blackbody represented by wavelength. This is the starting point of all infrared radiation theories, hence the blackbody radiation law.

Features of infrared thermometer: non-contact measurement, wide temperature measurement range, fast response speed, and high sensitivity. However, due to the influence of the emissivity of the measured object, it is almost impossible to measure the true temperature of the measured object, which is the surface temperature.