A method is described for ascertaining a group of at least two adjacently situated illumination units during the travel of a vehicle. The method includes a step of recognizing at least one first illumination unit and at least one second illumination unit in a detection range of a sensor and recognizing a subsequent departure of the first illumination unit from the detection range of the sensor. The method also includes a step of detecting a distance and/or a time which the vehicle travels after a departure of the first illumination unit from the detection range of the sensor up to a departure of the second illumination unit from the detection range of the sensor.