The best example I can come up with is Compton scattering. Here, you are colliding photons with an unbound particle, therefore one that does not have quantum en

The best example I can come up with is Compton scattering. Here, you are colliding photons with an unbound particle, therefore one that does not have quantum energy states. The quantum nature of light is shown by the fact that the degree of scattering depends upon the energy (and therefore wavelength) of the incident photon, and not on the intensity. If light were just a wave, then the effect would go away if the intensity were low enough.