Influence of the Increasing Drive Currents and Ambient Temperatures on the Performance of Different Chip Technology LEDs

Abstract

Proper heat management is necessary for better optical performance of high power light emitting diodes (LEDs). However, the thermal behavior of the LEDs differs as the chip technology changes. In this study, the InGaAlP and InGaN based amber and green LED were used to investigate the influence of different operating conditions on its thermal and optical performances. The increasing driving current affects the InGaN LED more than the InGaAlP LED. As the driving current increases, the green and amber LEDs loses its wall-plug efficiency (WPE) from 18.1 to 10% and 31.1 to 27.1% respectively. The higher drop in WPE of green LED was contributed by the higher junction temperature which rises more than 11.1°C than the amber LED. The RthJA was reduced around 4 K/W in green LED and only 1.9 K/W in the amber LED. However, the increasing ambient temperature give significant effect to the thermal behavior of the amber LED. As the ambient temperatures increases, the WPE of the amber LED reduces from 29.7 to 20.7% whereas the green LED loses its efficiency by 0.6%. By investigating the thermal and optical behaviors of the different chip LEDs under different operating conditions, the appropriate working condition of the LEDs at the optimum level can be identified.