The photoelectric effect is a phenomenon in which electrons are emitted from matter after the absorption of energy from electromagnetic radiation such as x-rays or visible light. The emitted electrons can be referred to as photoelectrons in this context. The effect is also termed the Hertz Effect, due to its discovery by Heinrich Rudolf Hertz, although the term has generally fallen out of use. Photoelectric effect takes place with photons with energies of about a few eV. If the photon has sufficiently high energy, Compton scattering(~keV) or Pair production(~MeV) may take place.