  The following work is motivated by the conceptual problems associated with
the wave-particle duality and the notion of the photon. Two simple classical
models for radiation from individual emitters are compared, one based on sines
with random phasejumps, another based on pulse trains. The sum signal is
calculated for a varying number of emitters. The focus lies on the final
signal's statistical features quantified by means of the temporal coherence
function and the temporal coherence length. We show how these features might be
used to experimentally differentiate between the models. We also point to
ambiguities in the definition of the temporal coherence length.
