The main causes of the rise in the starting voltage of the metal halide lamp are: the presence of free halogen (iodine, etc.) and the vapor phase metal halide causes the lamp voltage to rise. The gas phase halide and free halogen in the lamp have a certain saturation gas pressure at normal temperature, and their electron affinity in the discharge space is very strong. When the lamp is activated, the electrons emitted from the electrode are easily separated by free halogen (such as Iodine) is adsorbed and becomes a negative ion with a large mass. This negative ion is not easily accelerated by the electric field, thus reducing the number of ionization collisions. In this case, the voltage must be increased in order for the lamp to start smoothly.
After the lamp has been used for a while, the free halogen will further increase. This is due to the loss of both sodium and strontium during the lifetime (for sodium lamps): sodium migrates out of the arc tube due to the photoelectric effect, sodium migration causes iodine to remain and iodine is further increased; strontium and quartz glass bulbs can form silicic acid Salt and silicon halides. The introduction of impurities such as hydrogen and water into the lamp causes the lamp starting voltage to rise.
In the process of manufacturing the arc tube, it is easy to introduce impurities such as water and hydrogen, and these impurities are released when the lamp is started. When the lamp is discharged, hydrogen (water releases hydrogen when the lamp is discharged) can react with the metal halide to form hydrogen iodide. . Hydrogen iodide reduces electrons, causing the lamp to start to rise. Other factors (the electrode can not use a general oxide cathode, but the use of tungsten with higher work function than oxide) will cause the lamp to start high voltage.
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