The ratio of the luminance in candelas of the output phosphor to the input exposure rate in milliroentgens/sec defines:

The definition provides that the ratio of the luminance in candelas of the output phosphor to the input exposure rate in milliroentgens per second represents the conversion factor. This term is crucial in imaging as it quantifies the efficiency of an image intensifier in converting input radiation into visible light.

The conversion factor typically indicates how effectively the device transforms the x-ray input (in terms of a specific quantity like milliroentgens) to the output light seen on the screen (measured in candelas). A higher conversion factor signifies a more efficient image intensifier, which allows for better image quality while minimizing the required radiation dose to the patient.

Understanding this concept is essential in the context of radiology and fluoroscopy, where optimizing image quality and patient safety is paramount.