The Physics of Fluorescence: Implications for the Application and Evaluation of Alternative Excitation Light Sources

摘要

New light sources for exciting the fluorescence of magnetic particles and liquid penetrants are being introduced to the marketplace. Not all of them have the same spectral output as the ultraviolet sources that have been the mainstay of the industry. The fact that a light source provides an adequate reading on an ultraviolet radiometer is not itself a guarantee of performance, nor does adequate performance with one particle or penetrant guarantee satisfactory performance with all of them. There should be a rational basis for assuring that new sources will produce a fluorescent indication that is as at least as bright as that produced by the lights they are intended to replace. The key to performance is the spectral output of the light and its interaction with the excitation spectrum of the fluorescent indicating material. The underlying physics of fluorescence provide a theoretical basis for developing procedures to evaluate the performance of any light source with any particle/penetrant. We used this basis to implement two complementary measurement approaches for performance verification. One approach leads to a prediction of the efficacy of a light source relative to an industry-standard ultraviolet source, while the other is a direct comparative measurement procedure that confirms this prediction. This presentation will review the physical processes behind fluorescence and describe the measurement procedures that we have developed, and present results for several light sources in combination with a variety of fluorescent particles and penetrants.