Which inspection method uses UV light?

Dye penetrant testing is the correct choice because it specifically employs ultraviolet (UV) light as a means of identifying surface discontinuities in non-porous materials. In this method, a liquid penetrant is applied to the surface of a material, which seeps into any surface cracks or defects. After a given dwell time, the excess penetrant is removed, and a developer is applied. The developer draws out the penetrant from the cracks, making them visible under UV light. This illumination enhances the contrast of the penetrant against the surface, allowing inspectors to easily spot flaws.

The other methods mentioned do not utilize UV light. Magnetic particle testing involves the use of magnetic fields and iron particles to detect surface and near-surface flaws, while ultrasonic testing employs high-frequency sound waves to detect internal or subsurface flaws in materials. Visual inspection relies on the naked eye or basic magnification to identify defects without any specialized lighting techniques like UV. These distinctions emphasize why dye penetrant testing is uniquely suited for this UV light application.