Abstract: An illumination system includes a measurement stage, a light-providing part, a light-receiving part, and a processing part. The light-providing part includes light sources arranged in a dome shape, which irradiate incident lights to a measurement target on the measurement stage. The light-receiving part acquires reflection lights. The processing part controls the light sources to be turned on/off according to a dome-shaped sine wave pattern. The processing part controls the light sources to be sequentially turned on/off by shifting N times according to the dome-shaped sine wave pattern for a specific measurement position of the measurement target, and calculates a phase at the specific measurement position, an average of intensities of N reflection lights, and a visibility of N reflection lights, from intensities of N reflection lights. Thus, material of the measurement target may be easily determined.