1. A thermal radiation analysis method comprising the steps of, a) utilizing spectral acquisition means to acquire and measure a set of multiple spectral intensity distributions of a thermal radiation source radiating at multiple source temperatures at an effective spectral emissivity, wherein each of the spectral intensity distributions is associated with a particular source temperature, b) forming a first function of at least two of the measured spectral intensity distributions and of a set of temperature variables that represent the temperatures of the spectral intensity distributions used, such that said first function attains an extremum when the temperature variables equal the corresponding source temperatures, thereby calculating said source temperatures.