253.7nm wavelength is easily absorbed by the body, the main role of ultraviolet light in the biological DNA of the genetic material
Ultraviolet can make the DNA molecular bond rupture, resulting in bacteria can not breed and die. 
185nm wavelength can be oxygen in the air to produce ionized oxygen ions and free oxygen ions labile, combined with the oxygen in the air to produce Ozone
Strong oxidizing effect can kill bacteria effectively.
No need additonal chemicals, purely physical disinfection methods. 
No secondary pollution