The Leitz TruSens UV-C bulb for the Z-3000 and Z-3500 air filter is an indispensable part of the filter system. The growth of odour-causing microbes and floating organisms trapped in the air filters is reduced by the UV light. The UV waves also ensures that bacteria, viruses and protozoa are killed in the germ, preventing them from reproducing and infecting. This bulb is replaced on average every 2 to 3 years.