A colorimetric pyrometer is a type of radiation pyrometer. It is made according to the principle that the ratio of the radiation intensities of the two wavelengths in the radiation emitted by the heated object changes with the actual temperature of the object. The temperature of the heated object can be known by measuring the ratio of the radiation intensity at the two wavelengths. Compared with optical pyrometers, colorimetric pyrometers measure the temperature of the real object itself without correction.

The advantage of a colorimetric pyrometer is that the measured temperature value is very close to the true temperature. When used in environments with smoke, dust or water vapor, since these media have little difference in the light wave absorption characteristics of λ1 and λ2, the error caused by the absorption of the media is very small. For objects whose spectral emissivity is independent of wavelength (gray body), its true temperature can be directly measured. These advantages are not found in other types of pyrometers and infrared thermometers. It is still widely used in metallurgy and other industries.