Since the establishment of the International Temperature Scale of 1190 (ITS-90), much progress has been made in the development of radiometers and blackbody sources. Cryogenic electrical-substitution radiometry is widely used in detector and radiometer calibrations, and stable, high-temperature metal-carbon eutectic blackbodies are under development. Radiation thermometers can be calibrated for absolute radiance responsivity, and blackbody temperatures determined from the amount of optical power without the use of any fixed points to directly measure thermodynamic temperatures. These temperatures can be measured with lower final uncertainties than the ITS-90 derived temperatures. Just as the definition of the photometric base unit the candela, has been changed to one of optical power, the thermodynamic temperatures can be directly realized from optical power and length units.
blackbody radiation, freezing temperature, ITS-90, radiation thermometry, radiometry, thermodynamic temperature