Extracting phosphor-scattered photons to improve white LED efficiency

White light-emitting diode (LED) luminous efficacy must improve significantly if LEDs are to become useful for general lighting, Phosphors commonly used in white LEDs backscatter more than half of the down-converted light, of which a significant portion is eventually lost within the package, thus reducing the overall efficacy. This letter describes an experimental study that shows by placing the phosphor away from the die, the backscattered photons can be extracted and the efficacy can be significantly increased, At low currents, the luminous efficacy exceeded 80 lm/W. (c) 2005 WILEY-VCH Vorlag GmbH & Co, KGaA. Weinheim.