In the context of the COVID-19 pandemic, demand for air purifiers and air conditioners with air purification functions is increasing. Air purification technologies include those that use an electric discharge and those that use light. Among the air purification technologies using light, deep ultraviolet (UV) or UV-C is attracting attention as an effective measure for combating the novel coronavirus, because of its ability to inactivate and sterilize airborne and adhered viruses.