  The wave side of wave-photon duality, describing light as an electromagnetic
field (EMF), is used in this article. EMF of spontaneous light emission (SE) of
laser excited atom is calculated from first principles for the first time. This
calculation is done using simple method of atomic quantum electrodynamics. EMF
of SE is calculated also for three types of polyatomic light sources excited by
laser. It is shown that light radiated by such sources can be coherent, which
explains recent experiments on SE of laser excited atoms. Small sources of SE
can be superradiant, which also conforms to experiment. Thus SE is shown not to
be a random event itself. Random properties of natural light are simply
explained as a result of thermal excitation randomness without additional
hypotheses. EMF of SE is described by simple complex functions but not real
ones.
