A multi-method approach for beam characterization of microfading testers used in cultural heritage conservation science

Abstract Microfading testers have become widely accepted by the conservation science community for establishing and recommending appropriate lighting conditions that minimize damage to collections. These devices offer the opportunity of measuring the photostability of cultural heritage objects due to their optical setup, which allows to conduct and quantify accelerated photoaging over a spot of approximately 0.5 mm. Also, by using a high sensitivity photodetector it is possible to measure spectrocolorimetric change before it is perceived by the human eye. Although a considerable amount of testing is currently performed with these instruments, there are still safety concerns in terms of possible damage to the objects due to the use of a high intensity spot during testing. Nevertheless microfadeometry is widely considered a nondestructive technique. The advantages and disadvantages of several methods used to determine the beam shape and intensity profiles are described with the aim of providing various options to microfading researchers interested in characterizing their irradiation spots. Conventional and imaging methods were employed and are compared in terms of their accuracy, cost, reliability, and technical features. It has been found that both methods provide beam width measurements in satisfactory agreement within experimental error.