The experimental protocol was designed to ensure reproducibility of spectrometer and radiometer positioning and response.
Under the conditions of this test, lamp aging has been relatively slight. The average depreciation in germicidal fluence rates for all four lamps was 17% after 3980 h of operation. Slightly more depreciation was observed in the UVC than in the UVB region (18% versus 15% for the average of all lamps). Consistent with this, the germicidal fluence rate depreciated slightly more rapidly than the total (200 to 350 nm) fluence rate. These changes indicate a more rapid depreciation of the shorter wavelengths, but the extent to which this is due to inherent changes in the lamp spectra compared to solarization of the quartz sleeves cannot be determined from the present data. Efforts will be made to separate these two effects by examining the quartz sleeves at the end of the tests.