One or more electrons are ejected when a material is "hit" by light. This is called the photoelectric effect.
What happens is that light is made of photons; when a photon reaches the material's surface, it transfers its energy to the atom which is composing the material. If the photon has enough energy, one electron is torn off from the atom and gets ejected. With very energetic photons, it is possible that more than one electrons are ejected.
