Patent ID: 7538306

Claim:
An illumination device comprising a) an organic light-emitting diode ( 1 ) (OLED) having a light output that changes with use with b) an illumination area ( 2 ) and/or an active area ( 3 ), where light is being emitted for an illumination purpose, a reference area ( 4 ) being substantially smaller than the illumination area ( 2 ), wherein the reference area ( 4 ) is an isolated area ( 4 ) not connected to the illumination area ( 2 ) and/or active area ( 3 ), a substrate, on which the reference area ( 4 ), the illumination area ( 2 ) and/or the active area ( 3 ) are located, c) a driver ( 5 ) connected to the reference area ( 4 ), the illumination area ( 2 ) and/or the active area ( 3 ) to drive the reference area ( 4 ) separately from the illumination area ( 2 ) and/or the active area ( 3 ), with a measurement circuit ( 6 ) detecting at least one active value of the illumination area ( 2 ) and/or the active area ( 3 ) and at least one reference value of the reference area ( 4 ), a control circuit ( 7 ), which compares the active and the reference value and produces a correction signal in response thereto to compensate the changes in the light output of the illumination area ( 2 ), wherein the control circuit ( 7 ) calculates the correction signal for the illumination area ( 2 ) based on the active value and the reference value.