Patent ID: 8896237

Claim:
Method for operating a fluorescent lamp having a nominal power (WLa) and stabilized with an EM ballast (B) and supplied with a supply power comprising a supply voltage and supply current with current frequency (f) and current period (T), the method comprising the steps of, after starting and during normal operation, short-circuiting the lamp during an uninterrupted closing time interval (CTI) during each current period in order to operate the lamp at a reduced power, the method further comprising the steps of: detecting whether the lamp is stabilized by means of an inductive ballast in an L-system or stabilized by means of a capacitive ballast in an LC-system; if it is found that the lamp is stabilized by means of an inductive ballast in an L-system, setting the timing of the closing time interval (CTI) such that the closing time interval (CTI) is located entirely between two successive zero-crossings of the current; or if it is found that the lamp is stabilized by means of a capacitive ballast in an LC-system, setting the timing of the closing time interval (CTI) such that the closing time interval (CTI) has a first closing time segment (CTS 1 ) immediately before a zero-crossing of the current, having a first duration (Δ 1 ) higher than zero, and a second closing time segment (CTS 2 ) immediately after said zero-crossing of the current, having a second duration (Δ 2 ) higher than zero.