An illumination device is specified which includes a radiation source having at least one light-emitting diode, a control unit and a radiation receiving unit. The radiation receiving unit is provided, during operation of the illumination device for receiving both a radiation emitted by the radiation source and a reference radiation and for generating a measurement signal upon receiving the radiation from the radiation source and a reference signal upon receiving the reference radiation. An operating point for the radiation source is tunable by the control unit in a manner dependent on the measurement signal and the reference signal. Furthermore, a method is specified by which an emission characteristic of an illumination device can be adapted to a predetermined emission characteristic in a simplified manner.