Electrodeless gas discharge lamp having heat conductor disposed within magnetic core

#The invention relates to an electrodeless gas discharge lamp having a lamp vessel which is closed in a vacuum-tight manner and is filled with a metal vapor and a rare gas, the lamp comprising a core of a magnetic material in which a radio-frequency magnetic field is induceable by means of an electric supply unit and an electric field is generated, in the lamp vessel. The magnetic material core incorporates a member which is in contact with the core and consists of a heat-conducting material for discharging the heat generated in the core to the environment of the lamp. Such a lamp is disclosed in U.S. Pat. No. 4,017,764.

#In the Patent Specification an electrodeless discharge lamp is described having a lamp vessel in which an annular core of magnetic material, such as ferrite, is disposed around which a plurality of wire turns is provided, an electric field then being generated in the lamp vessel.

#In response to the discharge the temperature in the magnetic material core increases during operation of the lamp. In addition, the temperature in the core increases due to the occurrence of hysteresis phenomena in the magnetic material. It has been found that the intensity of the phenomena increases as a function of the temperature. There is then the risk that the permeability of the core material is reduced and the efficiency of the lamp decreases. It is conceivable that the lamp will fail.

#In the drawing

#FIG. 1 shows schematically a longitudinal section through a first embodiment of an electrodeless low-pressure mercury vapor discharge lamp.

#FIG. 2 is a cross-sectional view of the lamp of FIG. 1 along the plane II--II.

#The lamp shown in FIG. 1 comprises a glass lamp vessel 1 which is closed in a vacuum-tight manner and is filled with a quantity of mercury and a rare gas, for example argon. A luminescent layer 2 which converts the ultraviolet radiation generated in the lamp vessel into visible light is provided on the interior wall surface of the lamp vessel. In addition, the lamp incorporates a (rod-shaped) core 3 of a magnetic material (ferrite), provided in an induction coil 4. The core 3 and the coil 4 are arranged in a recessed portion 1a provided in the wall of the lamp vessel 1 near the longitudinal axis of the lamp. The coil 4 has a number of copper wire turns (for example seven) a small number (4a, 4b) of which are shown in the drawing. The coil 4 is connected to an electric power supply unit 5 by means of which a radio frequency magnetic field is induceable. In this embodiment supply unit 5 is disposed in the lamp. In specific embodiments however said unit 5 may be present outside the lamp. An electric field is then generated inside the lamp vessel 1.

#The core 3 contains a rod-shaped member 6 of a heat-conducting material for discharging the heat generated in the core during operation of the lamp. The member 6 extends over the central portion of the core 3 and along its overall length. In a cross-sectional view the surface area of member 6 is approximately 1/25 of the surface area of the ferrite core 3 (see FIG. 2). The member 6 consists of copper having a high thermal conductivity. Along its full length the rod is in an intimate contact with the core wall.

#At the bottom side the rod 6 is connected to a metal jacket 7, which also incorporates the electric power supply unit 5. The metal jacket 7 extends to the exterior side of the lamp (in order to discharge heat to the environment of the lamp) and comprises a sleeve 8 for fitting the lamp in a socket intended for incandescent lamps. A layer of electrically insulating material (not shown in the drawing) is provided between the sleeve 8 and the jacket 7.