Instead, a caesium iodide phosphor is deposited directly on the photocathode of the intensifier tube. This makes the photocathode very efficient at creating photoelectrons from photons. The photocathode releases electrons via the photoelectric effect as the incoming photons hit it. It consists of a photocathode, a microchannel plate, and an anode array. The light photons are then converted to electrons by a photocathode. The RCA prototype photomultipliers also used an Ag-O-Cs (silver oxide-caesium) photocathode. These photocathode devices do not detect temperatures, but rather infrared radiation variances. This tube consisted of a photocathode in proximity to a fluorescent screen. A photocathode usually consists of alkali metals with very low work functions. The micro-channel plate fits between the photocathode and screen.