Temperature dependence of the color rendering index of a phosphor-conversion white light-emitting diode

Guen-Hwan Ryu,Byungjin Ma,Han-Youl Ryu

doi:10.1063/1.5066351

Abstract

We experimentally investigated the temperature dependence of the color rendering index (CRI) of a phosphor-conversion (PC) white light-emitting diode (LED) composed of a GaN-based blue LED chip and yttrium aluminum garnet doped with Ce3+ (YAG) phosphor. For the 15 CRI values from R1 to R15, 12 CRI values were found to increase with temperature from 20 to 80 °C. The general CRI (Ra) was increased from 84.6 to 86.1 as the temperature increased from 20 to 80 °C. R9 which represents the color rendering property for the deep red was found to increase by more than 10% and some CRI values exhibited more than 20% increase in this temperature range. This increasing behavior of CRI with temperature is contrary to the case of a multi-chip-based white LED, where the Ra was reported to decrease with increasing temperature. The improvement in the CRI with temperature for the PC white LED is attributed to the relative increase of the spectral power distribution (SPD) in the wavelength range from 460 to 520 nm and the overall broadening of SPD with increasing temperature. As a result of the increase in the CRI with temperature, the PC white LEDs are expected to be advantageously used for stable high-temperature operation of LED lighting.

Highlights

The use of white light sources based on semiconductor light-emitting diodes (LEDs) have considerably increased in the general lighting and display applications owing to the high efficiency and eco-friendliness.1–3 The efficiency of white LEDs has been improved to a level that allows solid-state lighting to rapidly replace conventional lighting bulbs
The correlated color temperature (CCT) increased from 5922 to 6302 K, corresponding to the relative change of ∼6%. This temperature-variation in the chromaticity coordinates and CCT of the measured PC white LED is about half of the MC white LED in Ref. 14, implying that PC white LEDs with yttrium aluminum garnet doped with Ce3+ (YAG) phosphor are more stable to the temperature change compared with MC white LEDs
The general color rendering index (CRI) and all special CRIs of a PC white LED with YAG phosphors are found to increase with increasing temperature, which is firstly demonstrated in our experiments

Summary

INTRODUCTION

The use of white light sources based on semiconductor light-emitting diodes (LEDs) have considerably increased in the general lighting and display applications owing to the high efficiency and eco-friendliness. The efficiency of white LEDs has been improved to a level that allows solid-state lighting to rapidly replace conventional lighting bulbs. The PC white LEDs suffer from large Stokes’ shift loss They have become the mainstream in the LED market due to the simple structure, low cost, and relatively high luminous efficiency. The chromaticity point, correlated color temperature (CCT), CRI, and efficiency of LED-based light sources drift as the ambient temperature of the device increases. For a trichromatic LED-based MC white LED, it has been reported that the CCT increased from 6500 to 7200 K and the CRI decreased from 84 to 72 as the temperature increased from 20 to 80 ◦C.14 This large decrease in the CRI is attributed to the significant modification of spectral distribution from the optimum color condition with increasing temperature especially for a red LED. The experimental results of temperature-dependent CRIs of the PC white LED are analyzed based on the temperature dependence of spectral power distribution

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSION