The hand piece (30) has a temperature measuring device (34) e.g. pyrometer, measuring temperature in the hand piece or part of the hand piece for providing an electrical temperature signal. An electrical switching device (35) e.g. micro controller, is electrically connected with the measuring device and a signaling device (36) i.e. light source (47), to receive the temperature signal from the measuring device. The signaling device is switched between two signal conditions that differ from each other when the temperature signal reaches or exceeds or falls below a threshold value.
