The radiation intensity and wavelength from a blackbody at a given temperature T is governed by Planck's law . If the radiation intensity W b at a specific wavelength l is measured, the temperature T is the only unknown in the equation. As shown, the radiation intensity is a function of wavelength l and temperature T . For a given temperature, there is a particular wavelength associated with the maximum radiation intensity. This equation tells us what the most effective wavelength should be for measure a certain temparature T .
W b across the full wavelength range.
Note that the temperature T is the absolute temperature. When electromagnetic radiation impinges upon a surface of an object, the radiation is partially absorbed, partially reflected, and partially transmitted. If all of the electromagnetic radiation is absorbed by the object, the object is called a blackbody . Planck's law and the Stefan-Boltzmann law are derived assuming blackbody properties. Another term called emissivity is similar to emittance in describing the difference in radiation intensity between real materials and blackbodies.