Final answer:
The ratio of the number of light photons at the output phosphor to the number of x-rays at the input phosphor is known as the conversion efficiency.
Step-by-step explanation:
The ratio of the number of light photons at the output phosphor to the number of x-rays at the input phosphor is the conversion efficiency. This term is crucial in the field of medical imaging and radiology, where the conversion efficiency impacts the image quality and the dose of radiation received by the patient. It is also a key aspect of photomultiplier technology, where the photoelectric effect is utilized to convert light output into an electrical signal, effectively amplifying it. The efficiency with which this conversion occurs and the amplification takes place is vital in determining the sensitivity and the signal-to-noise ratio of the output.