Characteristics of spontaneous emission
This process has nothing to do with the external action. The radiation of each atom is spontaneous and independent. The photons emitted by them are different in the emission direction, polarization state and initial phase. And because there are more than one excited state of an atom, different atoms may be in different excited states, so the frequency of spontaneous emission is not single. The light emitted by ordinary light sources (such as incandescent lamps, fluorescent lamps, arc lamps, etc.) is mainly generated by spontaneous radiation.