Screens which absorb the energy in the x-ray beam that has penetrated the patient and convert this energy into a
light pattern which has as nearly as possible the same information as the original x-ray beam. The more
light a screen produces for a given input of x-
radiation, the less x-ray exposure and thus shorter exposure
time are needed to expose the film. In most film-screen systems, the film is sandwiched between two screens in a cassette so that the emulsion on each side is exposed to the
light from its contiguous screen.