The invention relates to a control system for at least two light tubes connected to a common transformer circuit. The control system comprises a control circuit which is provided with at least two detection inlets (a2, a3) used for detecting lamp currents (I1, I2) passing through the first and second light tubes, respectively. The detected lamp currents (I1, I2) can be regulated to a day mode with a high current intensity, and in a night mode with a low current intensity by the control circuit. The lamp currents (I1, I2) can be detected individually in day mode and in a common manner in night mode. The control system reduces instability of the tubes, in particular flicker.