Illuminance meter calibration with an LED spectrally tunable light source

Abstract

Calibration of an illuminance meter is indispensable for accurate measurement of the illuminance of indoor lighting and daylight. In recent years, because of the phasing-out of incandescent lamps and their replacement with LED lamps, it has become difficult to obtain an incandescent type standard lamp to calibrate an illuminance meter. To replace the standard lamp method, we constructed an illuminance meter calibration system based on an LED-based spectrally tunable light source. The approximate CIE Illuminant A spectrum realized by the LED-based spectrally tunable light source was controlled at various illuminance values (800–10,000 lx). A test illuminance meter was calibrated by comparison against a reference photometer with the realized approximate Illuminant A spectrum. The illuminance values measured using the reference photometer and using the test illuminance meter in the calibration system agreed within 2.5% without reference plane correction of the test illuminance meter, and within 1% with reference plane correction. Reference plane correction depends strongly on the measurement distance and the illuminance meter structure. This study demonstrated that it can be improved. Therefore, we infer that an illuminance meter calibration method using an LED-based spectrally tunable light source is a promising means of overcoming difficulties posed by the phasing-out of incandescent standard lamps.