As much as what percent of the film's darkening is due to light emitted by the intensifying screens?

• A. 95%
• B. 50%
• C. 75%
• D. 25%

Answer: (A)

In screen-film radiography, most of the film’s darkness comes from light produced by the intensifying screens. When X-rays strike the patient and then the screens, the screens convert that energy into visible light, which rapidly exposes the film’s silver halide crystals. The film emulsion is far more sensitive to visible light than to X-ray photons, so the light from the screens drives the vast majority of the density. That’s why about 95% of the film’s darkening is due to the light emitted by the screens, with only a small portion—roughly 5%—coming from direct X-ray exposure to the film. This relationship underlines how screens dramatically boost efficiency and allow lower patient doses while still producing a diagnostic image.