Optical and electrical characterization of breakdown processes in straight compact fluorescent lamps

摘要

The beginning of the 1980's saw the introduction of energy-efficient compact fluorescent lamps (CFLs), which for twenty years have proven their importance in the replacement of low-efficiency incandescent lamps. Today, further improvements of CFLs need a better knowledge of the physical processes underlying their working principles. One of the key points concerns ignition, as one of their limitations lies in the high-voltage pulses required for the lamp to start. Although the Townsend mechanism of electron avalanche is well known, its idealized description cannot be applied to the geometry of fluorescent lamps. In CFLs, the length between the electrodes is much longer than the tube diameter; therefore the wall plays an important role in the mechanisms of ignition. Early experiments reported the propagation of ionisation waves back and forth in the lamp during the early stages of electrical breakdown. However, all observations have been done in an indirect manner, i.e. with capacitive probes, Langmuir probes or fibre-coupled photomultipliers. It is only recently that global observations were carried out. This present study deals with optical and electrical diagnostics of the ionisation fronts that propagate within the lamp during the first phases of electrical breakdown. These observations are both time and space resolved in order to have a set of comprehensive data about the phenomena.