Nonclassicality of thermal radiation

It is demonstrated that stochastic c-number theories fail as a model of weak measurements on thermal radiation of low occupation numbers. This occurs, for example, at the wavelength of maximum irradiation in blackbody radiation. The classical model is approximately capable of describing weak measurements at high occupation numbers. The nonclassical effect is only present for quantum states with a negative Terletsky-Margenau-Hill quasi-probability distribution.