- The emission of electrons from a material exposed to electromagnetic radiation, especially in the infrared, visible, and ultraviolet regions. The frequency of the radiation must exceed a given minimum, or threshold frequency, for electrons to be emitted. Beyond this value, the energy of the emitted electrons depends on the frequency of the radiation. The greater the intensity of the incident radiation, the greater the number of liberated electrons.
- Any observed effect in which electromagnetic radiation, especially light, induces changes in the electrical properties of materials, surfaces, or regions exposed to it. These include the photoconductive effect, the photovoltaic effect, and the photodiffusion effect.