The present invention relates to an illumination device including a number of LEDs and a processor for receiving an input signal and generating an activation signal for at least one of the LEDs based on the input signal. The illumination device further comprises an LED driver for obtaining the voltage across and current through the LED. The processor may generate the activation signal based on the voltage, the current and a current-voltage model related to the LED. The current-voltage model defines a relationship between the current, the voltage and the colorimetric properties of light emitted by the LED. The present invention relates also to a method of controlling and a method of calibrating such an illumination device.