Photoelectric effect, also called as photoemission, is the production of electrons due to light energy falling on a material. Electrons emitted are called photoelectrons. 

Energy contained within the incident light is absorbed by electrons within the metal as they gain sufficient energy to be knocked out and gets emitted from the surface of the metal.
As proved by the classical Maxwell wave theory of light, the more intense the incident light is, the greater will be the energy with which the electrons gets emitted from the metal. It has been found that blue and violet lights emit maximum number of electrons from a metal surface due to their high energies, whereas red light is not sufficient to bring about this effect as it has less energy.