Abstract: A gas discharge lamp has a fill mixture with first radiation-emitting substances which emit predominantly in an ultraviolet spectral range, and a further radiation-emitting substance which has an emission line in a lower-frequency spectral range. The intensity at the lower-frequency emission line is monitored and used to control lamp operation. This prevents continued use of lamps whose normal service life has been exceeded, as evidenced by intensity dropoff or frequency drift. This in turn prevents damage to health, in lamps used for medical or cosmetic purposes, or malfunctions in technical manufacturing processes, in lamps used in such processes. Thus, irradiation with unsuitable discharge tubes is prevented. Depending upon the intended lamp application, preferred fill additives may include lithium, cesium, thallium, or sodium.