Fundamental interaction of the electromagnetic with substance generally results in solid radioactivity, even with the tiny degrees. The radiation of the majority of the matter with ultraviolet light or irradiation of shorter waves consequences in the discharge of electrons; some substances also demonstrate the phenomenon with visible radiation. This is titled as photo-emission. The energy of fotons is set free for the emitted electrons, that are addressed as fotoelectrons and are able to comprise a chain in an electrical circuit. The energy of electrons depends upon the absolute frequency of the light; its intensity level only affects the electron number emitted. These commentaries had taken mastermind Albert Einstein to more formulate the ideas of another great genius Max Karl Ernst Ludwig Planck on the theory of quantum.

The photo-emission led to the exploitation of the photocell, that is used with various objects, such as the attraction of solar power, production of systems of alarms against fire and robbery and drive of automated doors with remote control. Other photoelectrical effect are the photo conductivity and the photovoltaic effect. In the fotoconduction, the set free electrons behave inside as carrying of extra load of the material and thus the ohmic resistance lessens. This is particularly efficient in semiconductor units and the phenomenon is used in some devices to find the visible light not only as also the infrared emission. If the light comes about on certain sets of materials, as the selenium in a goal plate, and as they will be part of a completed electric circuit, will have a chain. This if gives because the light brings forth a eletromotriz force and the pair of materials if it becomes a cell; this is called photo-voltaic effect.

As base of many sensitive devices to the light, this is one of the presently used rules to try to use to reward the solar energy in the electrical energy yield.