Fluorescent lamp cathodes: Voltage-controlled preheating characteristics

The paper provides a method for measuring the emission time for the voltage-controlled preheating mode of a fluorescent lamp cathode. The method is based on monitoring the lamp voltage. The paper presents the difference between the thermionic emission curves obtained by the method based on the ratio of hot to cold coil resistance (Rh /R c ) and by the lamp voltage monitoring method. It is supposed that the R h /R c method curve is mainly influenced by the heterogeneous cathode heating. The cathode is composed of the filament coil and the emissive material, the specific heat capacities of which differ. It is believed that this difference makes it difficult to create a thermal balance in the whole cathode when the emissive coating reaches the emission temperature at a time soon after the initial current surge. This makes it difficult to describe the thermionic emission characteristics dynamically by the Rh/R c method. An equation is proposed for the thermionic emission curve provided by the lamp voltage monitoring method. Energy supplied to the cathodes until the emission time is reached is examined in terms of the average resistance of the cathode.