“…A typical illumination system is composed of the light source, the color mixing system, integral components, the beam splitter prism, and the micro-display panel [5,6]. Employing LEDs as light sources, a number of studies have been mainly focused on the integral components, including light pipes [7], lens arrays [8], compound parabolic concentrators [9], or gradual enlarging tapered light pipes [10,11], with few of them paying enough attention to the color mixing system. However, the color mixing system deserves additional attention, because it also plays an important role in determining the optical performance and the compactness of the projection system.…”