An illumination device comprising a plurality of light emitting diodes (LEDs) and a method for calibrating the illumination device is provided herein. According to one embodiment, the method may include subjecting a first LED to a first ambient temperature, measuring a forward voltage developed across the first LED upon applying a relatively small drive current to the first LED, detecting at least a first, a second and a third luminous flux output from the first LED upon successively applying at least a first, a second and a third drive current to the first LED, and storing results of the measuring and detecting steps within the illumination device to calibrate the first LED at the first ambient temperature. In some embodiments, the first LED may be subjected to a second ambient temperature, which is different from the first ambient temperature, and the method may repeat the steps of measuring, detecting and storing to calibrate the first LED at the second ambient temperature.