Dear All: I'm trying to use fluctuation dissipation theorem to describe spontaneous photon emission process by electron-hole recombination in semiconductor material. I notice that all the references using such a method considers the dipole's degree of freedom separately, for example in x, y, z direction separately, and then sum together. Does this means that the actual total energy of the oscillator in 3D space is 3ħω? But for after the emission of one electron-hole pair the photon's energy is just ħω. How to understand this?