An apparatus and method for operating a light generator (2) with a voltage source (4) makes possible a simple and reliable determination of the light generator's condition. The apparatus provides (a) a device (5; 13) for generating a measurement voltage the voltage present at ale light generator (2), (b) device (6, 9) for generating a first and a second comparison voltage, each proportional to the current flowing through the light generator (2), (c) a device (9, 8) for forming a difference voltage from the measurement voltage and one comparison voltage and a summation voltage from the measurement voltage and the other comparison voltage, (d) two capacitive rectifiers (7) for rectifying the difference voltage and the summation voltage, and (e) a controller (3), by which the rectified difference voltage and the rectified summation voltage can be evaluated.