The propagation of the first ionization wave in a compact fluorescent lamp (T4 tube with standard electrodes) during ignition was investigated for various initial dc-voltages (both polarities measured against ground) and gas compositions (with and without mercury). In addition the effect of the presence of a fluorescent powder coating was studied. The propagation velocity of the initial wave was measured by an assembly of photomultipliers installed along the tube, which detected the light emitted by the wave head. The propagation was found to be faster for positive than for negative polarity. This effect is explained involving processes in the electrode region as well as in the wave head. Waves propagate faster in the presence of a fluorescent powder coating than without it and gases of lighter mass show a faster propagation than gases with higher mass.
A new method for the determination of the cathode fall voltage of
fluorescent lamps is shown. The cathode fall voltage can be determined by
measurement of the lamp operating voltage at constant lamp wall temperature,
constant discharge current and variation of the electrode heating current.
Commercial lamps, which do not need to be specially prepared, can be used for
the measurement. The results show good correlation to other measurements of
the cathode fall voltage at various discharge currents by means of
capacitive coupling. The measured values of the cathode fall voltage are
used for determining the minimum, target and maximum setting of the sum of
the squares of the pin currents of one electrode (the so-called SOS value)
as a function of the discharge current in fluorescent lamp dimming.
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