During medical diagnosis the patient stands between the X-ray machine, or other radiation source, and the fluorescent screen.
Radiation passes through the body, producing varying degrees of light and shadow on the screen.
Although the regular X-ray photograph shows more detail, fluoroscopy is preferable when the physician wants to see the live image, i.e., observe the size, shape, and movement of the patient's internal organs. In industry the fluoroscope is used for the examination of materials, manufactured objects, welds, castings, and other objects, principally for flaws.