Extracting phosphor‐scattered photons to improve white LED efficiency

Abstract

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 experi‐mental study that shows by placing the phosphor away from the die, the backscattered photons can be extracted and the ef‐ficacy can be significantly increased. At low currents, the lu‐minous efficacy exceeded 80 lm/W. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Reliability and Lifetime Prediction of Remote Phosphor Plates in Solid-State Lighting Applications Using Accelerated Degradation Testing

“…[1][2][3][4] It has been already shown that thermal stress degrades the luminous output of the devices. [15][16][17][18][19][20][21][22][23] This study aims at studying the effect of blue light intensity together with thermal stress on the lumen depreciation and the reliability of LED-based products and on the acceleration of optical degradation. The phosphor layer can itself be a heat generator as the input power increases and becomes more important if there is not a sufficient thermal path for heat dissipation.…”

“…[1][2][3][4][5][6][7][8][9][10] In this type of LED, the phosphor is either coated on the chip or mixed with the lens disc. [11][12][13][14][15][16][17][18][19][20][21][22] The spatial distribution of phosphor in white LED lamps strongly influences the colour uniformity and the efficiency of the light source. In proximate phosphor distributions, the phosphor is located in close proximity to the semiconductor chip, while in the remote phosphor configuration, there is a distance between the phosphor layer and the chip.…”

“…Application of both thermal stress and light intensity in a HAST set-up is expected to make the kinetics of degradation much faster. There are many papers regarding the reliability of LED systems [13][14][15][16][17][18][19][20][21] under thermal stress; however, there is limited information available about the effects of combined blue light intensity and thermal stress on the ageing and the reliability of remote phosphors. In this study, the effects of both stress factors, applied in the HAST set-up, are studied.…”

Inorganic Phosphor Materials for Lighting

“…They could suffer from saturation based quenching due the long decay time of 2 E ? 4 A 2 , but this issue can be virtually eliminated by using a remote phosphor configuration reducing the incident radiation flux [176]. The thermal stability for K 2 TiF 6 :Mn 4?…”

Effects of Graphene Monolayer Coating on the Optical Performance of Remote Phosphors

“…In such a system, the phosphor layer can be either deposited directly on the chip or incorporated into a lens disk. [9][10][11][12][13] Moreover, white LEDs are multipart systems. Apparently, each of these components can break and induce failure, leading to a reduction of light intensity and even early failure before the expected lifetime of the instrument.…”