Patent ID: 8339386

Claim:
An electroluminescent (EL) device, comprising: an illumination area comprising one or more primary EL emitters; a reference area comprising a reference EL emitter; a reference driver circuit configured to cause the reference EL emitter to emit light while the EL device is active; a sensor configured to detect light emitted by the reference EL emitter; a measurement unit configured to detect an aging-related electrical parameter of the reference EL emitter while the reference EL emitter is emitting light; and a controller configured to: receive an input signal for each primary EL emitter in the illumination area, form a corrected input signal from each input signal using the detected light and the aging-related electrical parameter, and apply the corrected input signals to the respective primary EL emitters in the illumination area, wherein the reference driver circuit is further configured to cause the reference EL emitter to emit light at two levels, a measurement level and a fade level, at different times, and wherein the measurement unit is further configured to take measurements of the reference EL emitter while the reference EL emitter emits light at the measurement level.