Electrodes

Electrodes in LTI’s mercury xenon lamps are made of tungsten; this is the only metal with a sufficiently high melting temperature and sufficient vapor pressure at elevated temperatures to be used for electrodes. Compact arc lamps require solid tungsten electrodes because of their high wattage concentration and correspondingly high plasma temperatures within the short arc gap directly between the electrodes.

The smaller, pointed electrode is called the cathode, which supplies the current to the lamp and facilitates the emission of electrons. To supply a sufficient amount of electrons, the cathode material is doped with thorium. The optimum operating temperature of the cathode tip is approximately 2000 degrees C. To obtain this precise operating temperature, the cathode tip is pointed and in many cases has a groove on the pointed tip to act as a heat choke. This heat choke causes the tip to run at a higher temperature. This configuration of the cathode tip allows for a very high concentration of light from the cathode tip and a very stable arc.

The anode, the larger electrode, receives electrons emitted by the cathode. Once the electrons penetrate the anode face, the resulting energy is converted to heat, most of which radiates away. The large, cylindrical shape of the anode helps to keep the temperature low by radiating the heat from the anode surface. LTI’s anode material is specially treated to ensure long life with minimal melting or change in the anode shape.