If an electron is in an excited state it can return to a lower energy level. When it does this, it loses energy. The amount of energy it loses will be equal to the difference in the energy levels ...

Studying the line spectra produced by hot gases and absorbed by cooler gases allows us to identify the elements in stars. When a gas is very hot, it doesn’t emit all wavelengths of light.

The plasma emission can, therefore, be resolved both spectrally and temporally to yield spectra containing the atomic emission lines corresponding to the atoms present in the plasma volume.