A multi-channel array spectrometer combines a spectral measurement system and a reference detector which measures photometric or radiometric qualities. High accuracy photometric or radiometric measurement of a wide dynamic range can be achieved by correcting measurement results of the reference detector with a spectral correction factor. The multi-channel array spectrometer comprises a bandpass filter wheel holding a set of bandpass filters and an open hole. The wheel is placed between an entrance slit and gratings. A test light beam passes through a turret of the bandpass filters. The test light beam can be precisely measured band by band. The spectrometer can also quickly and accurately measure a plurality of test light sources having similar spectral characteristics by using the stray light correction factor.