the question of whether em radiation can be treated as a classical em wave or as a collection of photons is entirely dependent upon whether the number of photons collected in a measurment is large or small if its large then the classical treatment i e spectral radiance over infinitesimal frequency bands will apply planck's law as stated in the article calls a spectral radiance which immediately implies a classical em wave no reference needed photonic emission is for any em radiation where the number of photons collected is small including planck's law in certain cases broadband means the radiation is spread out over a relatively wide bandwidth narrowband means it is not broadband is not necessarily photonic nor is narrowband necessarily classical em its not a matter of how spread out the radiation is its a matter of how many photons are collected in a measurement broadband can be classical em if many photons are collected narrowband can be photonic if only a few are collected