Lighting and signalling device of an automobile and operating method of such a device

The method involves activating a first optical system (3) intended to generate a first light beam e.g. dipped beam or fog light. Operating conditions of the first optical system are fixed, so that the first optical system produces a second light beam. A second optical system (4) intended to generate a third light beam is activated, where the generated third and second light beam are in union to form a day light signaling beam. An independent claim is also included for a lighting and signaling device for a motor vehicle, including an optical system.