Yes, I never understood why light was considered 'particles' :-(
As far as I understand it is because light can only be emitted by atoms with discrete energy levels, but (IMHO again) light is emitted by atoms with discrete energy levels because it is emitted when electrons jumps from one energy level to another and that the possible trajectory of electrons around the atoms aren't continuous, I don't see how this is related to the nature of light..
I think that with an [undulator](https://en.wikipedia.org/wiki/Undulator) you can tune "continuously" the energy of the light emitted: in the webpage it is written "the emitted radiation is coherent with a wavelength determined by the period length and the beam energy", but as the precise relationship between the beam energy and the wavelength produced isn't specified I'm not 100% sure..
As far as I understand it is because light can only be emitted by atoms with discrete energy levels, but (IMHO again) light is emitted by atoms with discrete energy levels because it is emitted when electrons jumps from one energy level to another and that the possible trajectory of electrons around the atoms aren't continuous, I don't see how this is related to the nature of light..
I think that with an [undulator](https://en.wikipedia.org/wiki/Undulator) you can tune "continuously" the energy of the light emitted: in the webpage it is written "the emitted radiation is coherent with a wavelength determined by the period length and the beam energy", but as the precise relationship between the beam energy and the wavelength produced isn't specified I'm not 100% sure..