Recently, solid state lighting has begun to play an important role in colorimetric instrumentation. LEDs are being evaluated as one of the possible standard light sources for such devices. In this study, an innovative tunable daylight simulator is developed, which mainly consists of only a few LEDs and a specially designed optical thin-film filter with a fixed transmission spectrum. This simulator is able to simulate daylight spectra with correlated color temperatures ranging from 4000 to 10,000 K with very good color rendition indices (CRI≧97). We have achieved the color difference 0.01, which is better than 0.015, a maximum tolerance as defined by the International Commission on Illumination of the color differences in 1976 u'v' color space between standard daylight and a simulator.