Cathode fall measurements in fluorescent lamps

We describe an improved method and apparatus for making capacitive measurements of the cathode fall in fluorescent lamps employing known behaviour of anode oscillations to provide a zero-of-potential reference, placing the entire cathode and anode fall waveform on an absolute rather than relative scale. The improved method is applicable to any diameter of fluorescent lamp currently manufactured. We also describe a method and apparatus for making spectroscopic measurements of the cathode fall in fluorescent lamps. This uses the abrupt onset of emission of certain selected spectral lines of the rare gas filling as a signal that the cathode fall has exceeded the excitation potentials of the spectral lines in question.