Effects of Filter and Burner Aging on the Spectral Power Distribution of Xenon Arc Lamps

Abstract

Solarization caused by aging of the borosilicate glass filters used for xenon arc lamps has a very large effect on the short wavelength ultraviolet radiation emitted by the lamps, even with strict control of irradiance. If irradiance is precisely controlled at a constant mid UV wavelength, filter aging causes significant reductions in short wavelength UV and increases in long wavelength UV and visible light intensities. If irradiance is controlled in a broad band which includes long wavelength UV, filter aging will cause changes in short wavelength UV, even when the broad band irradiance is kept constant. Differences in short wavelength UV transmission between different lots of the same type of filter can cause very large changes in short wavelength UV emission of the lamp when aged filters are replaced. The differences in UV transmission between different lots of glass persist even after aging. Changes in the spectral power distribution of the xenon lamp caused by filter aging can have a significant effect on the rate of polymer or product degradation and may be a major cause of the variability in results between different devices running identical test cycles. Changes in xenon lamp spectral irradiance caused by aging of the xenon burner are much smaller than the changes caused by filter aging. Xenon burners used in high irradiance cycles may show larger losses of short wavelength UV emmissions than burners used in cycles controlled to produce lower irradiance.