The increased brightness of an image resulting from accelerated electrons traveling across to the output phosphor is called "flux gain." Flux gain is the term used to describe the increase in the number of light photons that are emitted from the output phosphor screen of an image intensifier tube compared to the number of electrons that originally struck the input phosphor. This gain in brightness is a key advantage of using image intensifiers in various imaging applications such as night vision devices and medical imaging systems.