In this work, we report on a new monitoring method for an organic light-emitting diode (OLED) panel for lighting by optical sensing of the wave-guided light in the substrate. Using microlens array films, the wave-guided light was extracted into the edge or back side of the panel to be monitored by a photodiode. The luminance of the extracted light was measured as linearly proportional to the front light. Thus, by converting the extracted light into photo voltage, monitoring the luminance change occurring in the OLED is possible. Based on the results and concepts, we have proposed a photodiode-equipped driving circuit which can generate compensated driving current for uniform luminance of OLED panels.