The brightness of the fluorescent indication is affected by which factor controlled by the inspector?

• A. Concentration of the dye on the surface
• B. Intensity of the UV light
• C. Capability of the dye to absorb UV light
• D. Efficiency of the dye in converting UV to visible light

Answer: (B)

Brightness in this method comes from fluorescence: the dye absorbs ultraviolet energy and then emits visible light. The amount of visible light you see—and thus how bright the indication appears—depends mainly on how much UV energy you deliver to the surface. Increasing the UV lamp intensity raises the excitation level, making indications brighter (within safe and equipment limits). The dye’s ability to absorb UV light and its efficiency in turning that energy into visible light are intrinsic properties of the dye and aren’t something you adjust during the test. Similarly, the dye concentration on the surface is set by the penetrant and application process, not something you control to change brightness in real time. Therefore, the factor controlled by the inspector that most directly affects brightness is the intensity of the UV light.