Which instrument is used to determine the intensity of fluorescent penetrants after preparing a thin film?

• A. A caliper
• B. A fluorometer
• C. A spectrometer
• D. A densitometer

Answer: (B)

Measuring how bright the fluorescent penetrant glows requires a device that excites the dye and directly senses the emitted light. A fluorometer is designed for this purpose: it uses a specific excitation light to trigger fluorescence in the penetrant and then measures the resulting emission intensity, giving a quantitative readout of how strong the fluorescence is. This makes it the best choice for evaluating the penetrant in a thin film.

A caliper only measures dimensions, not light output. A spectrometer can analyze the light spectrum and its intensity but isn’t the standard tool for directly quantifying fluorescence in a prepared film; it’s more about spectral characteristics than a straightforward intensity readout. A densitometer measures optical density, not fluorescence, so it wouldn’t reflect the fluorescence strength of the penetrant.