The term “electroluminescence” is usually taken to mean the direct conversion of electrical energy into light by solid “phosphors”, which are mostly crystalline inorganic materials capable of luminescence under a number of different forms of radiation, for example ultraviolet, and α, β, γ and X rays. Electroluminescence has been studied for 20 years, but its use in lighting is quite recent, and its application to detectors, converters and amplifiers of radiation is the subject of current research. The radiology application is one of these latest possibilities. There are several reviews of electroluminescence in recent literature (Destriau and Ivey, 1955; Zalm, 1956; Henderson, 1958) and only a brief outline will be given here. The practical construction mostly used is in the form of a parallel plate capacitor with the powdered phosphor incorporated in a solid organic dielectric C (Fig. 1). To allow the light to issue from this cell, one electrode B is a transparent conducting film on the glass plate A on ...