Lumen Depreciation Diagnosis in Modulated LED Lighting Systems

Lumen depreciation is the condition that the light output of a light emitting diode (LED) lamp falls below a fraction of its peak output. In LED lighting systems with multiple LED lamps, lumen depreciation leads to undesired distortions in the rendered illumination distribution. Automatic diagnosis of lumen depreciation in LED lighting systems is thus an important problem. We propose an approach to diagnose lumen depreciation in individual LEDs using photosensors by modulating the LED lamp output with a unique identifier and encoding average drive current within, and a carrier sense multiple access on the optical channel. At the photosensor, the received signal is processed in the electrical domain. The average drive current corresponding to an individual LED lamp is extracted and a residual is computed with respect to a nominal value. A threshold detector based on testing the mean change of the residual signal is used to diagnose lumen depreciation of the LED lamps.