What is the main purpose of using a black light during fluorescent penetrant inspection?

During fluorescent penetrant inspection, a black light is used primarily to make the indications visible. This technique involves applying a fluorescent penetrant to the surface being inspected, which can seep into any surface discontinuities such as cracks or porosity. After allowing the penetrant to dwell for a specified period, excess penetrant is removed, and a developer is applied to draw out the remaining penetrant from the flaws.

The black light, which emits ultraviolet (UV) light, causes the fluorescent dye in the penetrant to glow brightly. This fluorescence helps inspectors easily identify and evaluate the size and significance of any defects present, which may be difficult to spot under normal lighting conditions. This property of fluorescence is crucial as it enhances the visibility of imperfections that need to be addressed, thereby ensuring the integrity of the inspected material.

The other choices do not align with this primary function. While enhancing lighting conditions may seem relevant, the main purpose of the black light goes beyond mere illumination. It does not measure crack depth and does not contribute to cleaning parts; instead, it specifically serves to enhance the visibility of the defects highlighted by the fluorescent penetrant.