The invention relates to a control system for at least two light tubes (6, 7) connected to a common transformer circuit (5). The aim of said invention is to prevent in a relatively simple manner the instability of the tubes, in particular a flicker thereof. The inventive control system (2) comprises a control circuit (3) which is provided with at least two detection inlets (a2, a3) used for detecting lamp currents (l1, l2) passing through the light tubes (6, 7) The detected lamp currents (l1, l2) can be regulated to a day mode with a high current intensity and to a night mode with a low current intensity by means of the control circuit (3). The lamp currents (l1, l2) can be detected individually in day mode and in a common manner in night mode.