The present invention relates to a lighting device, as well as to a lighting system comprising such a lighting device and an adjustable power source, and also relates to a method of driving such a lighting system. The lighting device comprises at least one LED (1a, 1b), a control device that comprises a measuring means (7, 9) to measure a quantity that is indicative of an electrical resistance of said LED at a predetermined current or voltage, a power supply control means (11) connected to said measuring means (7, 9) and constructed to control an adjustable electrical power supply (3a, 3b) for driving the LED (1a, 1b), said signal being based on said value of said quantity. The electrical resistance of a LED is functionally dependent of the LED's junction temperature, which in turn determines its optical output characteristics. Thus, by measuring the junction temperature indirectly, through measuring of electrical LED characteristics, and mapping them to a temperature, LED output control is possible.