Cathode luminescence refers to the phenomenon of light generation from the cathode of a vacuum tube or a cathodoluminescent material. Synonyms for cathode luminescence include field emission, cold cathode emission, and secondary electron emission. Field emission is the emission of electrons from a surface due to the influence of an external electric field. Cold cathode emission is the emission of electrons from a cathode oxide layer at room temperature. Secondary electron emission refers to the emission of electrons from a material when it is bombarded by energetic particles, typically electrons, ions, or photons. All these phenomena give rise to the generation of light from cathodoluminescent materials.