The photoelectric effect is a phenomenon in which electrons  are emitted from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as "photoelectrons".As it was first observed by Heinrich Hertz in 1887, the phenomenon is also known as the "Hertz effect", although the latter term has fallen out of general use. Hertz observed and then showed that electrodes illuminated with ultraviolet light create electric sparks more easily.

The photoelectric effect takes place with photons with energies from about a few electronvolts to, in high atomic number elements, over 1 MeV. At the high photon energies comparable to the electron rest energy of 511 keV, Compton scattering, another process, may take place, and above twice this (1.022 MeV) pair production may take place
Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave–particle duality.

The term may also, but incorrectly, refer to related phenomena such as the photoconductive effect (also known as photoconductivity or photoresistivitity), the photovoltaic effect, or the photoelectrochemical effect which are, in fact, distinctly different.
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