What does "black light" refer to in the context of PT?

In the context of Liquid Penetrant Testing (PT), "black light" specifically refers to ultraviolet (UV) light that enhances the visibility of fluorescent indications. When a fluorescent penetrant is applied to a material, it seeps into any surface flaws and is designed to fluoresce when exposed to UV light. This fluorescent glow is crucial for detecting surface defects, as it stands out against the non-fluorescent background. The use of a black light allows inspectors to easily identify these indications, making the inspection process more efficient and effective. This emphasizes the importance of using appropriate lighting conditions to ensure accurate results during PT inspections.