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

M Yazdan Mehr,G Q Zhang,W D Van Driel

doi:10.1007/s11664-015-4120-y

Abstract

A methodology, based on accelerated degradation testing, is developed to predict the lifetime of remote phosphor plates used in solid-state lighting (SSL) applications. Both thermal stress and light intensity are used to accelerate degradation reaction in remote phosphor plates. A reliability model, based on the Eyring relationship, is also developed in which both acceleration factors (light intensity and temperature) are incorporated. Results show that the developed methodology leads to a significant decay of the luminous flux, correlated colour temperature (CCT) and chromatic properties of phosphor plates within a practically reasonable period of time. The combination of developed acceleration testing and a generalized Eyring equation-based reliability model is a very promising methodology which can be applied in the SSL industry.

Highlights

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
If the phosphor is placed away from the Light emitting diodes (LEDs) chip at a relatively large distance, which is called a remote phosphor configuration, the probability of light emitting from the phosphor and directly hitting the low-reflectivity LED chip becomes significantly lower, leading to a significant improvement in the phosphor efficiency
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

Summary

Introduction

Light emitting diodes (LEDs), made by combining phosphor with blue light sources, are the most commercially available solid state light (SSL) sources.[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. SSL devices are normally based on a blue chip, combined with yellow phosphor, and are typically in the range of 4500–8000 K correlated colour temperature (CCT). Recent development strategies are based on the production of white LEDs in the lower (Received June 23, 2015; accepted October 1, 2015; published online November 5, 2015)

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