Brighter and smarter LEDs via graded refractive indexes

LEDs are the next-generation lighting source. However, their efficiency and the uniformity of the illumination they produce is limited by the large contrast between the refractive index (n) of the LED semiconductor (n = 2.5–3.5) and air (n = 1). The resulting total internal reflection (TIR) gives planar-surface LEDs a very low light-extraction efficiency (LEE). In addition, the emission pattern has a peak emission intensity along the LED surface normal with decreasing intensity away from the surface normal, which provides uneven illumination.