Circuit arrangement for alternately switching on and off at least two light strings connected electrically in parallel for a vehicle headlamp, comprising - a parallel circuit, having at least two luminous strings connected electrically in parallel, each luminous string comprising a number of light sources connected electrically in series with one another - at least one energy source for supplying the parallel circuit, wherein a first of the at least two luminous strings (2, 3) connected electrically in parallel has a working range with a voltage lower limit and a voltage upper limit for operating the first luminous string and wherein a second of the at least two luminous strings (2, 3) connected electrically in parallel has a working range with a voltage lower limit and a voltage upper limit for operating the second luminous string, wherein the voltage upper limit of the first luminous string is below the voltage lower limit of the second luminous string, the first luminous string being connected in series with a switching element, the circuit arrangement being set up to bring about a change in the operation of at least two strings (2, 3) on the basis of the presence of only a single external switching signal (Sext), in that the parallel circuit is connected to the energy source in such a way and/or the energy source is designed in such a way - that in a conductive state of the switching element the voltage applied to the parallel circuit is within the operating range of the first luminous string and thereby the first luminous string is switched on and the second luminous string is switched off, and - in that, in a non-conducting state of the switching element, the voltage applied to the parallel circuit is raised towards the operating range of the second luminous string and thus the first luminous string is switched off and the second luminous string is switched on. - a parallel circuit, having at least two luminous strings connected electrically in parallel, each luminous string comprising a number of light sources connected electrically in series with one another - at least one energy source for supplying the parallel circuit, wherein a first of the at least two luminous strings (2, 3) connected electrically in parallel has a working range with a voltage lower limit and a voltage upper limit for operating the first luminous string and wherein a second of the at least two luminous strings (2, 3) connected electrically in parallel has a working range with a voltage lower limit and a voltage upper limit for operating the second luminous string, wherein the voltage upper limit of the first luminous string is below the voltage lower limit of the second luminous string, the first luminous string being connected in series with a switching element, the circuit arrangement being set up to bring about a change in the operation of at least two strings (2, 3) on the basis of the presence of only a single external switching signal (Sext), in that the parallel circuit is connected to the energy source in such a way and/or the energy source is designed in such a way wherein a first of the at least two luminous strings (2, 3) connected electrically in parallel has a working range with a voltage lower limit and a voltage upper limit for operating the first luminous string and wherein a second of the at least two luminous strings (2, 3) connected electrically in parallel has a working range with a voltage lower limit and a voltage upper limit for operating the second luminous string, wherein the voltage upper limit of the first luminous string is below the voltage lower limit of the second luminous string, the first luminous string being connected in series with a switching element, the circuit arrangement being set up to bring about a change in the operation of at least two strings (2, 3) on the basis of the presence of only a single external switching signal (Sext), in that the parallel circuit is connected to the energy source in such a way and/or the energy source is designed in such a way - that in a conductive state of the switching element the voltage applied to the parallel circuit is within the operating range of the first luminous string and thereby the first luminous string is switched on and the second luminous string is switched off, and - in that, in a non-conducting state of the switching element, the voltage applied to the parallel circuit is raised towards the operating range of the second luminous string and thus the first luminous string is switched off and the second luminous string is switched on.