A single 1" borosilicate glass collimating lens at the exit port is standard on the 201-100 and TH3 lamp housings. This lens not only improves light collection efficiency to f/1.5, but also filters harmful UV rays while allowing visible and IR light to pass through (λ>360nm). For the 201-100 arc lamp housing, it also acts as a safety window should the high pressure arc lamp explode inside the housing. This option upgrades the borosilicate glass to fused silica such that UV wavelengths (λ>200nm) can pass through as well. Please note that some UV lamps produce dangerous levels of ozone and should be enclosed inside the lamp housing.