It has been discovered experimentally that light emitted by layers of photoexcited dye molecules or quantum dots deposited on metallic thin films is spatially coherent. Identifying the physical origin of this spatial coherence is a difficult task in the absence of a systematic procedure to model theoretically the field correlation function of the photoluminescence. The presence of strong coupling and the presence of delocalized plasmonic modes have been considered as possible candidates to explain the origin of the spatial coherence. Here, we use a general coherence-absorption relation recently derived to address this question.