What we have here is the SPT 2102 UV Bulb, the replacement bulb for the SPT AC 2102 Heavy Duty Air Cleaner. The combination of UV ray and TiO2-coated filter produces Photo Catalytic Oxidation (PCO). This process creates hydroxyl radicals and super-oxide ions, which are highly reactive electrons. These electrons aggressively combine with other elements in the air, such as bacteria and volatile organic compounds (VOC), which are harmful pollutants. Once bound together, the chemical reaction takes place between the super-charges ion and the pollutant, effectively burning the pollutant. This breaks the pollutant down into harmless carbon dioxide and water molecules.