Method for operating a tail light of a motor vehicle, wherein the tail light has, in particular in addition to a functional light source assigned to at least one further light function, a rear light source assigned to a rear light function having a plurality of luminous regions (8, 9, 10) that can be controlled independently with respect to the operation and the brightness, wherein at least one environment sensor (13, 14) of the motor vehicle records sensor data describing other, following road users in the area behind the motor vehicle, characterized in that, when at least one switch-on criterion evaluating the sensor data and checking for the presence of at least one further road user within a predefined distance range of the rear of the motor vehicle is fulfilled, a brightness-increasing switching process, in particular switching on and/or dimming up, of a second luminous region of the rear light source previously not in operation or operated with less brightness than at least one other, first luminous region (8, 9) is performed in such a way that the total emitted brightness of a portion of the tail light comprising at least the rear light source remains constant, wherein - the portion comprises only the rear light source, wherein, in order to compensate for the increase in brightness of the at least one second luminous region, at least one first luminous region (8, 9) has its brightness reduced, or - the portion comprises, in addition to the rear light source, the or at least one functional light source of the tail light, wherein, in order to compensate for the increase in brightness of the at least one second luminous region, the at least one functional light source has its brightness reduced. characterized in that, when at least one switch-on criterion evaluating the sensor data and checking for the presence of at least one further road user within a predefined distance range of the rear of the motor vehicle is fulfilled, a brightness-increasing switching process, in particular switching on and/or dimming up, of a second luminous region of the rear light source previously not in operation or operated with less brightness than at least one other, first luminous region (8, 9) is performed in such a way that the total emitted brightness of a portion of the tail light comprising at least the rear light source remains constant, wherein - the portion comprises only the rear light source, wherein, in order to compensate for the increase in brightness of the at least one second luminous region, at least one first luminous region (8, 9) has its brightness reduced, or - the portion comprises, in addition to the rear light source, the or at least one functional light source of the tail light, wherein, in order to compensate for the increase in brightness of the at least one second luminous region, the at least one functional light source has its brightness reduced. - the portion comprises only the rear light source, wherein, in order to compensate for the increase in brightness of the at least one second luminous region, at least one first luminous region (8, 9) has its brightness reduced, or - the portion comprises, in addition to the rear light source, the or at least one functional light source of the tail light, wherein, in order to compensate for the increase in brightness of the at least one second luminous region, the at least one functional light source has its brightness reduced.