Light collection systems for multiple LED arrays

Light emitting diode (LED) has numerous advantages such as long lifetime, large color gamut, small size and the absence of mercury vapor and thus there has been recognition that LED could be an alternative light source for projection display application. Due to its compact size, LED is a very attractive RGB light source for portable projectors. To improve the brightness of the projector, it is very critical to improve the light collection efficiency of the RGB LED light sources. In this work, traditional compound parabolic concentrator (CPC) was designed and its performance was studied. The CPC has a high collection efficiency, but its size is too bulky to be used in the portable projectors. Hence, a freeform collection system was designed and optimized to gain a compact size which can be used in the portable projectors. After optimization, it has a collection efficiency of 85%, slightly lower than that of the traditional CPC. But its diameter of the output aperture is 13.4 mm, 36% smaller than that of the traditional CPC and its length is 25 mm, 58% shorter than that of the traditional CPC. Meanwhile, the divergence angle of the freeform collection system is ±10° which is smaller than that of the designed traditional CPC. Hence, the freeform collection system may be used as the collimator in the portable projection display application.