Light-emitting diodes have become increasingly common in recent times, and users are continuously finding new applications for LED light, which provides unique features such as color-tunable illumination. The color of illumination is easily tuned because LED sources may be integrated with small color LED chips, and their color output may be manipulated without inefficient filters. The color controllability of LEDs is very attractive in applications such as downlighting, spot lighting, and entertainment, architectural, floodlight, and show lighting, where a narrow beam is projected at a distance. It is not surprising that almost every entertainment stage, building, and monument is now brightly lit with colored LED light.
However, multicolor-chip LEDs are non-homogeneous color sources. When projection optics are added, undesirable patterns such as spatial and angular inhomogeneities or strong color separation usually appear. Simultaneous light projection and color mixing is challenging because most collimators separate colors, and most color mixers spread the light beam. Recently, we proposed and demonstrated novel optics for multicolor LED spotlights that used a short, straight, highly reflective lightpipe, a thin volume scattering diffuser, and a compact total internal reflection (TIR) collimating lens.1 Another newly developed optics system uses minilenses arranged on both the outer and the inner surfaces of a hollow dome that covers the LED chips.2,3 This dome mixes colored light, which can then be collimated using additional optics. Although these optics mix and project colored light at a distance, they are secondary optical elements that are added to the encapsulating package.