How is the intensity of fluorescent penetrants determined?

• A. A thin film is achieved by dipping filter paper into penetrant, drying it, and using a fluorometer with reference standards
• B. Measuring UV light intensity
• C. Qualitative visual comparison
• D. Amount of dye smeared on the surface

Answer: (A)

The main idea is that fluorescence intensity is quantified by measuring the emitted light with a fluorometer and comparing it to calibrated reference standards. In practice, a thin film of penetrant is prepared on a carrier (such as filter paper) so a known amount is analyzed, and the fluorometer reads the fluorescence at a specific wavelength. The reference standards provide a consistent scale, allowing you to translate the measured signal into a comparable intensity value that indicates how strongly the penetrant’s fluorescence—and thus the flaw indication—appears. Measuring just UV light intensity, performing only a qualitative visual check, or basing the assessment on how much dye is smeared on the surface do not give a calibrated, quantitative measure of defect-related fluorescence.