In order to provide an illumination system for line illumination with a minimal intermediate gap between adjacent elongated trunks, which gap is maintained minimal over length of time, a coupling member is implemented and arranged for longitudinally connecting the elongated trunk in line with an adjacent further elongated trunk thereby forming a self-sustained trunked illumination system, with the coupling member having a first coupling portion to be fixed with the elongated trunk at its second trunk end portion thereof, as well as a second coupling portion structured to engage with the adjacent further elongated trunk at its first trunk end portion, the second coupling portion arranged in setting a gap distance between the two elongated trunks between a first configuration, wherein the gap distance is extant and a second configuration, wherein the gap distance is minimal, by imparting a tension force on the further elongated trunk in a longitudinal direction towards the first elongated trunk.