All objects with a temperature higher than absolute zero are constantly emitting infrared radiation energy to the surrounding space. The infrared radiation characteristics of an object—the magnitude of the radiation energy and its distribution by wavelength—has a very close relationship with its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, its surface temperature can be accurately determined, which is the objective basis for infrared radiation temperature measurement.

The influence of object emissivity on radiation temperature measurement: the actual objects existing in nature are almost not black bodies. The radiation amount of all actual objects depends not only on the radiation wavelength and the temperature of the object, but also on the type of material constituting the object, the preparation method, the thermal process, the surface state and the environmental conditions. Therefore, in order to make the law of black body radiation applicable to all practical objects, a proportional coefficient related to material properties and surface states must be introduced, that is, emissivity. This coefficient indicates how close the thermal radiation of the actual object is to the black body radiation, and its value is between zero and a value less than 1. According to the law of radiation, as long as the emissivity of the material is known, the infrared radiation characteristics of any object are known.