Method and device for driving a gas discharge lamp

Driver for operating a fluorescent lamp having a nominal power (WLa), the driver comprising:

• lamp output terminals for connecting to respective lamp electrodes (3ab, 4ab) of the lamp;
• an EM ballast (B) connected in series with at least one lamp output terminal, the EM ballast (B) comprising a series arrangement of an inductor (L) and a capacitor (C);
• an electronic switch (S) connected in parallel to said lamp output terminals;
• a control circuit for controlling the electronic switch;
• wherein the control circuit is designed, after starting and during normal operation, to control the electronic switch (S) such as to short-circuit the lamp during an uninterrupted closing time interval (CTI) during each current period in order to operate the lamp at a reduced power, wherein the timing of the closing time interval (CTI) is such that the closing time interval (CTI) has a first closing time segment (CTS1) immediately before a zero-crossing of the current, having a first duration (Δ1) higher than zero, and a second closing time segment (CTS2) immediately after said zero-crossing of the current, having a second duration (Δ2) higher than zero.

Lamp system, for accommodating two fluorescent lamps of mutually the same type, each lamp having a nominal power (WLa), the system comprising individual lamp drivers for each lamp, each driver comprising:

• lamp output terminals for connecting to respective lamp electrodes (3ab, 4ab) of the corresponding lamp;
• an EM ballast (B) connected in series with at least one lamp output terminal, each ballast (B) comprising an inductor (L);
• an electronic switch (S) connected in parallel to said lamp output terminals;
• a control circuit for controlling the electronic switch;
• wherein a first one of said ballasts is a substantially capacitive ballast comprising a series arrangement of said inductor (L) and a capacitor (C);
• wherein the control circuit associated with this first ballast is designed, after starting and during normal operation, to control the corresponding electronic switch (S) such as to short-circuit the lamp during an uninterrupted closing time interval (CTI) during each current period in order to operate the lamp at a reduced power, wherein the timing of the closing time interval (CTI) is such that the closing time interval (CTI) has a first closing time segment (CTS1) immediately before a zero-crossing of the current, having a first duration (Δ1) higher than zero, and a second closing time segment (CTS2) immediately after said zero-crossing of the current, having a second duration (Δ2) higher than zero;
• wherein a second one of said ballasts is a substantially inductive ballast;
• wherein the control circuit associated with this second ballast is designed, after starting and during normal operation, to control the corresponding electronic switch (S) such as to short-circuit the lamp during an uninterrupted closing time interval (CTI) during each current period in order to operate the lamp at a reduced power, wherein the timing of the closing time interval (CTI) is such that the closing time interval (CTI) is located entirely between two successive zero-crossings of the current at terminates at such zero-crossing.