Why is the autonomous UVD Disinfection Robot so effective?

From the UV radiation emitted by the sun, UV-A, UV-B reach the earth’s surface. However the UV-C light is completely absorbed by the earth’s athmosphere, therefore microorganisms did not develop any natural resistance againts the it. All microorganisms, viruses, bacteria get inactivated in a couple of seconds if radiated by the UV-C light. The UVD Robot can inactivate the MERS, SARS, Covid-19 virus in 20 seconds while the robot is in motion.