What type of light is commonly used in fluorescent dye penetrant testing?

In fluorescent dye penetrant testing, ultraviolet (UV) light is commonly utilized because it excites the fluorescent dye particles that have been applied to the surface of the test material. When the dye penetrates any cracks or defects, it becomes luminescent when exposed to the UV light, making these flaws much easier to detect against the background of the material.

The use of UV light enhances the visibility of the fluorescent dye, which emits a bright glow under UV illumination. This property allows inspectors to identify even minute surface defects that might otherwise be invisible under normal lighting conditions. Therefore, the combination of a fluorescent penetrant and UV light makes it an effective and sensitive method for non-destructive testing.

In contrast, while normal white light and visible spectrum light can illuminate a surface, they do not provide the same level of contrast or sensitivity for detecting the fluorescing penetrant. Infrared light is not suitable for this application because it does not excite the fluorescent compounds used in the testing process. Thus, the correct choice emphasizes the critical role of UV light in effectively performing fluorescent dye penetrant testing.