Patent ID: 8719998

Claim:
A surface cleaning apparatus comprising: a housing for movement along a surface to be cleaned; a suction nozzle associated with the housing and having a nozzle opening directed at the surface to be cleaned; a vacuum source associated with the housing and in fluid communication with the suction nozzle via a working air conduit; a recovery chamber in fluid communication with the vacuum source and the working air conduit whereby material drawn into the suction nozzle by the vacuum source is deposited into the recovery chamber; a stain sensing system directed at the surface to be cleaned and comprising: a visible light-emitting element; an ultraviolet (UV) light-emitting element; and at least one light reader for detecting light intensity as reflected from the surface to be cleaned when light is emitted from the at least one of the visible and UV light-emitting elements; and a controller for receiving a signal representative of the light received by the at least one light reader; wherein the controller receives a first signal representative of the light reflected from the surface to be cleaned by the visible light-emitting element and a second signal representative of the light reflected from the surface to be cleaned by the UV light-emitting element; and wherein the controller determines a differential value between the first signal and the second signal and compares the differential value to a predetermined threshold value.