How is the sensitivity level of fluorescent penetrant measured?

• A. In terms of brightness
• B. By dye concentration
• C. By penetration depth
• D. By inspection time

Answer: (A)

In fluorescent penetrant inspection, how sensitive the process is depends on how bright the fluorescent indications appear under UV light. Sensitivity is effectively a threshold for detection: the brighter the fluorescence that can be seen, the more sensitive the test is to faint or small flaws. Practically, this sensitivity is described or calibrated by comparing the observed brightness to a reference standard or scale under standardized UV lighting. So the measure comes down to the emitted light intensity, i.e., brightness.

Dye concentration, penetration depth, and inspection time influence what you may see, but they aren't how sensitivity is defined or measured. The key concept is the brightness of the fluorescent signal under the same viewing conditions.