Abstract: A driver waveform (30) for a gas discharge lamp is produced by a ballast circuit. The waveform (30) has a substantially vertical rising portion 831) forming an instantaneous, of time 10 &mgr;secs or so between T0 and T1, transition between currents −I1 and +I1 which are at a current value less than peak currents IP. Then in a transition rise at controlled slew rate the waveform (30) rises with a straight rising portion (32) to a steady peak current IP identified by the numeral (33). The peak current IP is maintained between T2 and T3 which accounts for between 40% and 80% of the cycle time. Then at T3 decline occurs with waveform having a declining slew rate portion (34) to time T4 when instantaneous transition between time T4 and T5 and currents +I1 to −I1 occurs. The driver waveform reduces the formation of high frequency harmonies and increases are stability.

Abstract: The electronic ballast may be fitted to a wide variety of third party lamps and is usually controlled to allow for a variety of light settings. A simple ballast circuit is provided in which both the ignition and regulation functions are carried out by the same inductor. This removes a switching stage resulting in better efficiency. The ignition energy of the lamp is progressively built up which helps reduce Radio Frequency Interference and reduces Electrical Magnetic Interference and reduces wear on the lamp components.

Abstract: A fault detection apparatus for a public lighting system has a number of lamps. Each lamp incorporates an operating and control circuit which will emit signals on a fault occurring or conditions arising indicating a potential fault, for example, of a gas discharge tube forming part of the lamp. The apparatus, which can be incorporated in the lamp operating and control circuit or be provided as a separate plug in unit incorporates a host interface. A control unit and an externally visible signalling device such as a flag or flashing beacon will allow the detection of a fault or potential fault for example during normal daylight hours.