I was working with high-pressure sodium (HPS) lamps. In the begining of my thesis I sought to introduce the readers to the photometric basics and the phisical phenomena of discharges, to be familiar with the unknow expression. My project was to search for the most typical failure of this product and eliminate it. During the research I was measuring the geometrical dimension and the material quality of the ceramic tube, as well as the electrical and thermical parameters of the arctube, to find the root of this failure. After the basic tests, the initial goals changed. These tests showed that the examined ceramics are weaker than the ceramics of the other manufacturers, but maybe it will be able to use it. Therefore the priority of the ispection which can filter the worse ceramics got lower, and the elimination of the failure became higher priority. For the research I was using mass spectrometer, optical and elektron microscope, digital multimeter, thermocouple and X-ray. I sorted the different issues in a logical structure with a operation sequence and finally I found root of this failure. I give instructions to eliminate this failure mode.