  The intensity of the monochromatic radiation that is used to generate the photoelectric effect has no influence on the speed with which the electrons are ejected from the metal but affects only the frequency  of this process. Even with intensities so weak that on the classical  theory hours would be required before the electromagnetic energy  passing through a given atom would attain to an amount equal to that  of a photon, the effect begins immediately, the points at which it  occurs being distributed irregularly over the entire metal plate.  This fact is a proof of the existence of light quanta that is no less meaningful than the flashes of light on the scintillation screen are  for the corpuscular-discontinuous nature of \(\alpha\)-rays.