Temperature and measurement: comparison between two models of nonequilibrium radiation

We generalize a previous proposal of an experiment (J. Fort, D. Jou, J.E. Llebot, Physica A 248 (1998) 97) that, on the basis of predicted corrections to the Planck spectral law, may allow to determine experimentally what quantity is measured by a thermometer in steady-state nonequilibrium systems composed of matter and radiation. We include the photon number flux as an additional constraint. According to the model presented, the differences between the spectra predicted from two possible temperature definitions are higher than previously thought. In contrast to some previous papers, our model does not consider a specific matter content for the system.