Abstract: To detect defects in a continuously moving strip of transparent material, especially a wide thin glass strip, a narrow monochromatic light beam is guided transverse to the motion direction of the moving strip and is coupled into the moving strip, preferably through an edge region of the moving strip, by a transparent liquid arranged between the moving strip and the light source producing the monochromatic light beam. In a first embodiment the monochromatic light beam is inclined to an upper surface of the moving strip through which it passes and is coupled into the moving strip by a transparent liquid whose index of refraction is greater than that of the atmosphere surrounding the moving strip. In a second embodiment the monochromatic light beam is parallel to the upper surface of the strip and is coupled into an edge surface of the continuously moving strip by a transparent liquid whose index of refraction is about equal to that of the moving material.

Abstract: A glass or glass ceramic cooking top 1 has on its underside 6 at least one heating unit 7. The heating unit 7 is in flat, heat-conducting contact with the underside 6, and contains an electrical resistance heating element exhibiting PTC behavior, the temperature in zone 3 being limited to a desired value without the use of a temperature limiter.