Einstein's photo electric effect & compton effect establish particle nature of light. These effects can be explained only, when we assume that the light has particle nature (To explain, Interference & diffraction the light must have wave nature. It means that light has both particle and have nature, so it is called dual nature of light).
KEmax=Ephoton−Wo
The above equation supports:
Ephoton=hv
It proves that light is in the form of dicrete packets of energy and not wave.
Otherwise the light with lower frequency than the threshold could give enough energy(slowly accumulate) to the electrons to come out of the metal.
Hence this theory supports particle nature of light, as suggested by Einstein.