References(11) Cited-By(2) High-frequency fluorescent lamp operation requires proper cathode preheating by electronic ballasts incorporating a preheating function. This paper examines minimum thermionic emission curves for three different ways of measuring emission times. One is based on a lamp ignition test, another on the ratio of hot to cold coil resistance (Rh/Rc), and the third on the lamp voltage monitoring. The observation that the emission time measured by the lamp ignition method tends to be shorter than that measured by the lamp voltage monitoring method in a short preheat time may be understood in terms of the relaxation of the limited thermal conductivity of the emissive material due to the initial flow of the discharge current. We do not believe that the shorter emission time measured by the lamp ignition method causes premature thermionic emission. On the other hand, when the duration of the heterogeneous heating in a cathode is negligible, then the Rh/Rc method may be used as well. This paper points out that the average resistance of a standardized cathode over the period up to the emission time should be regarded as a substitution resistor. Furthermore, a maximum curve similar to the minimum preheating requirement curve, being examined to replace the maximum preheating broken lines for the present requirement in the IEC, is helpful for determining a new coming maximum required energy line. In the last part of this paper, an approach to the standardization by a preheating energy line together with a suitable value for the substitution resistor is supported.
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