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

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 Ce ³⁺ (YAG) phosphor. For the 15 CRI values from R ₁ to R ₁₅ , 12 CRI values were found to increase with temperature from 20 to 80 °C. The general CRI (R _a ) was increased from 84.6 to 86.1 as the temperature increased from 20 to 80 °C. R ₉ 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 R _a 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.