Provided is a method of sensing an illuminance in a passive matrix organic light emitting diode display, the display including a plurality of lower electrode patterns arranged in parallel, a plurality of transparent electrode patterns arranged in parallel and being perpendicular to the lower electrode patterns, and an organic compound layer interposed between the lower electrode pattern and the transparent electrode pattern, the method comprising steps of: (a) forming a predetermined voltage difference between at least one electrode patterns of the transparent electrode patterns as anodes and the lower electrode patterns as cathodes; (b) measuring the magnitude of current formed by the transparent electrode pattern and the lower electrode pattern in the step (a); and (c) measuring an illuminance using the measured current, in which a voltage supplied to the lower electrode pattern is relatively higher than that of the transparent electrode pattern in the step (a).