Which light is used to view fluorescent penetrants?

Which light is used to view fluorescent penetrants?

• A. Ultraviolet (black) light
• B. Visible white light
• C. Infrared light
• D. X-ray light

Answer: (A)

In fluorescent penetrant inspection, the dye in the penetrant is designed to glow when it absorbs ultraviolet energy and then emits visible light. Ultraviolet light, specifically UV-A (often called black light), provides just the right energy to excite the fluorescent dye so cracks and surface flaws glow brightly against a dark background. Visible white light won’t cause that glow because it doesn’t efficiently excite the dye, so indications remain hard to see. Infrared light and X-ray imaging are used for different inspection methods and don’t induce fluorescence in the penetrant. In practice, you illuminate the part with UV-A in a dim or dark room and observe the surface—the fluorescing indications reveal defects clearly. Do keep in mind that UV exposure can be harmful, so use proper eye protection and shielding.

In fluorescent penetrant inspection, the dye in the penetrant is designed to glow when it absorbs ultraviolet energy and then emits visible light. Ultraviolet light, specifically UV-A (often called black light), provides just the right energy to excite the fluorescent dye so cracks and surface flaws glow brightly against a dark background. Visible white light won’t cause that glow because it doesn’t efficiently excite the dye, so indications remain hard to see. Infrared light and X-ray imaging are used for different inspection methods and don’t induce fluorescence in the penetrant. In practice, you illuminate the part with UV-A in a dim or dark room and observe the surface—the fluorescing indications reveal defects clearly. Do keep in mind that UV exposure can be harmful, so use proper eye protection and shielding.