Electric, magnetic and mixed generalised radiance tensors are proposed for describing the emission properties of planar sources of stationary random electromagnetic fields in any state of spatial coherence and polarization. Radiometric quantities such as the generalised radiant emittance and intensity, and the polarization parameter of the field are determined with basis on the generalised radiance tensors. These quantities reduce to their scalar counterparts if the vector character of the field is not regarded. In addition, the generalized radiance was analyzed using a procedure which separates the contributions provided by individual radiators from those provided by radiator pairs within their immediate surrounding, subjected to the accomplishment of conservation laws. This procedure reveals that only the individual radiators of the planar source contribute to the measurable radiometric quantities; the correlations of the field vectors in the surrounding of each individual radiator only modulates its contribution; and that modulations redistribute the contributions given by the individual radiators which can be understood like a lateral flux over the wavefront. Finally, the mixed generalised radiance tensor gives new insight about the physical meaning of the Poynting theorem. In this framework, interference is understood as resulting from the addition of positive and negative energies provided by the spatial coherence properties of the field onto the incoherent emission of the source.
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