The invention relates to a light source (1) having at least two semiconductor light-emitting elements (21, 22, 23, 24, 210, 211, 212), wherein the semiconductor light-emitting elements (21, 22, 23, 24, 210, 211, 212) emit light of different color. The light emitted by the semiconductor light-emitting elements (21, 22, 23, 24, 210, 211, 212) is coupled into a light conductor (3), at least partially, wherein the coupled-in light exits laterally from the light conductor (3). The brightness of the semiconductor light-emitting elements (21, 22, 23, 24, 210, 211, 212) can be adjusted by means of a control electronics (5). A light sensor (7) is arranged such that the light sensor (7) receives the light coupled in from the semiconductor light sources (21, 22, 23, 24, 210, 211, 212) and exiting laterally from the light conductor (3). The control electronics (5) having a light sensor (7) is designed to accumulate the sensor signals over an integration time interval, and to compare the accumulated signals of the light sensor (7) with a target value or a target range, and to change the brightness of the semiconductor light-emitting elements (21, 22, 23, 24, 210, 211, 212) depending on the difference of the sensor signals to the target value or target range, and to change the integration time interval subject to the distance of the sensor signal to the target value or the target range, or subject to a change in the target value.