UV SYSTEMS, Inc. has new data on the solarization of SW Hoya Optics U-325C filters. The Smithsonian Institution National Museum of Natural History has two fluorescent mineral displays in which they use UV SYSTEMS, Inc. SW TripleBright II model FSLS UV lights. Because of solarization the Smithsonian normally replaces the filters in their UV lights about every year.
They recently sent UV SYSTEMS, Inc. two filters from one TripleBright II to have their transmission measured. We know when those filters were installed and when they were removed, and because they turn “on” and “off” their fluorescent displays at the same time every day (except Christmas) we can calculate the exact number of hours those two filters were exposed to SW UV. Those two SW FS-60 filters were exposed for exactly 5695 hours. Those used filters had a transmission of 21.2% for one and 25.1% for the other.
UV SYSTEMS, Inc. usually recommends that SW filters be replaced when their transmission is below half of what a new filter would be (between 28.5% and 30% transmission). New FS-60 filters have a transmission of about 56.9% to about 60% at 253.7 nm (SW). Based upon the Smithsonian data, SW filters used in a SW TripleBright II or TripleBright 3 UV lights should be replaced about every 4900 hours.