Recent progress in thermodynamics of radiation - exergy of radiation, effective temperature of photon and entropy constant of photon

The recent progress on thermodynamic properties of spectral radiant energy in the field of thermodynamics of radiation is reviewed. The effective temperature of photon T-lambda representing the energy quality of photon is introduced. The relation between T-lambda and the wavelength lambda is given as lambda T-lambda =c (3)=5.33016x10(-3) m.K. The entropy constant of photon is given as s(lambda) =3.72680x10(-23) J/K. The exergy, entropy and enthalpy of the spectral blackbody radiation, the equilibrium cavity radiation, the radiation flux in open system are discussed by using T-lambda and s(lambda) , as well as the entropy change in the process of the state transformation of photon gas. By analyzing the exergy of spectral radiation, the exergy efficiency of spectral radiant energy available for photosynthesis is proved to be higher than that of light energy. The method for the irreversible loss of exergy calculation in radiant energy converters is also discussed.