Abstract: The present invention relates to a driver for driving a gas discharge lamp. In use, the tips of a conventional lamp's electrodes are subject to tip growth and tip destruction, resulting in decreased or increased arc length, respectively. This has an undesirable effect on the light output of the lamp. The driver of the present invention includes a controller for controlling a current source to the electrodes of the lamp whereby parameters of the current are varied in such a way that tip growth and tip destruction are alternated. As a result, arc length variations stay within certain limits over the lifetime of the lamp.

Abstract: A driver (1) for driving a gas discharge lamp (2) comprises: a controllable current source (3); a controller (4) for controlling the current source (3); measuring means (5) for measuring the distance between the lamp electrodes (21, 22). The controller controls the current source (3) such as to generate a commutating lamp current with a predefined current frequency (f) and a duty cycle (?). The controller is capable of operating in a modulated duty cycle mode in which the duty cycle has a first value (?1) during a first phase (P1) alternated with a second value (?2) equal to one minus the first value (?2=1??1) during a second phase (P2), wherein the second phase (P2) and first phase (P1) have mutually equal duration, and wherein switching between the second phase and first phase and vice versa occurs at a predefined duty cycle switching frequency (f?).