a disinfection chamber coupled to a propulsion system configured for moving along a surface to be disinfected, said disinfection chamber defining a closed distal end, an open proximal end and a surrounding wall having opposing front and rear portions and opposing side portions,

a radiation source mounted inside the disinfection chamber for irradiating said surface through the open proximal end;

the wall of the disinfection chamber defining a peripheral shielding impervious to the radiation;

the propulsion system comprising a peripheral seal surrounding a proximal edge of said wall and being configured to obstruct radiation that might otherwise escape from inside the disinfection chamber,

at least one light sensor inside the disinfection chamber configured to monitor visible light penetrating into the disinfection chamber through the open proximal end; and

a control device coupled to the at least one light sensor and responsive to visible light entering through the proximal end of the chamber for turning off the radiation source.