SCREEN LAG refers to:

• A. Static electricity
• B. Focal spot blur
• C. Phosphorescence/afterglow
• D. Light diffusion

Answer: (C)

Screen lag is the lingering light emitted by the radiographic screen after exposure, caused by phosphorescence or afterglow of the phosphor. When the screen is hit by X-rays, the phosphor stores some energy in traps within its crystal lattice and then releases it slowly as light even after the exposure has ended. This continued emission can expose the film and create a ghost image on subsequent radiographs. This phenomenon is distinct from static electricity, which involves charge buildup; focal spot blur, which is geometric unsharpness from the tube’s focal spot size; and light diffusion, which relates to light spreading during exposure but not the lingering afterglow that causes lag.