Stray light rejection for spectral UV irradiance measurements using a combined monochromator-spectrograph measuring instrument.

Critical UV applications such as disinfection and dermatological treatments call for the need for accurate UV spectral irradiation measurements. Due to poor stray light rejection, single monochromators and spectrographs are not able to provide a satisfying accuracy. For critical measurements, a scanning double monochromator offers a much better solution. In this project, a combination of a single monochromator with a large bandpass and a spectrograph has been developed and it has been shown that this apparatus has stray light rejection characteristics even better than those obtained with a commercially available high-accuracy scanning UV-VIS double monochromator system. The UV irradiance of several light sources is determined using both instruments and the stray light contributions are discussed.