An apparatus is disclosed for inspecting a surface containing a material that emits luminescent radiation in response to absorbing excitation radiation. The apparatus comprises a laser disposed in or adjacent to a housing. A sensor opening is defined in the housing and permits emission of excitation radiation generated by the laser and permits admission of the luminescent radiation emanating from the surface in response to the excitation radiation. A sensor monitors whether ambient light is being admitted between an edge of the sensor opening and the surface upon which the sensor opening is in contact. A safety circuit permits the laser to be actuated only when the sensor detects a substantially or completely light-impermeable contact between the edge of the sensor opening and the surface.