Which statement correctly describes fluorescence emission range?

• A. The emitted light falls in the visible range, about 400-700 nm
• B. It is emitted in the ultraviolet range
• C. It is emitted in the infrared range
• D. It is emitted as gamma rays

Answer: (A)

Fluorescence emission is at longer wavelengths than the light that excites it, so when a fluorescent penetrant is excited with ultraviolet light, the glow produced is in the visible spectrum. In practice, UV excitation (often around 365 nm) causes the dye to emit visible light, typically somewhere in the 400–700 nm range, which is what inspectors look for with appropriate lighting and filters. This is why the emitted light being in the visible range is the correct description. Emission in ultraviolet, infrared, or gamma rays would not match the typical fluorescence behavior used in penetrant inspection.