The electron density and temperature in the Philips QL-lamp

There is an increasing interest in electrodeless lamps since reactions between the electrodes and the plasma are avoided which leads to a considerably longer life time and less restrictions to the choice of filling than conventional discharge lamps. One special class of electrodeless lamps is that formed by the inductive fluorescent lamps. For some years commercial lamps of this type have been available: the QL-lamp of Philips since 1992 and the Genura of General Electric since 1994. Recently the third major lighting company Osram Sylvania announced the Endura. Within the Eindhoven University of Technology a 2D model is being developed which accurately describes the QL-lamp. The electron density and temperature are key-parameters in the description of the plasma. Moreover it appears that due to the relatively high gas temperature (550 to 800 K, depending on the filling pressure) and electron density the mercury ground state atoms are seriously depleted in the most active zone of the discharge.