A comparative study for the junction temperature of green light-emitting diodes

Abstract

Solid-state lighting devices offer a wide variety of color options applicable for general and automotive lighting, various display systems, and a number of niche applications. As they get smaller, generated heat fluxes become more intense and induce serious lifetime and performance issues. Although the light output from light-emitting diodes (LEDs) is the most efficient at a narrow optical spectrum compared with conventional lighting sources, they are still not adequate to satisfy consumer demands due to considerable amounts of lost energy and emerging thermal issues. On the other hand, it is possible to achieve effective thermal solutions if the junction temperature of LEDs is precisely determined. A number of techniques have been proposed for the junction temperature measurement of LEDs such as forward voltage change and infrared (IR) thermal imaging. In this study, green LEDs were studied to observe optothermal interactions using a number of proposed junction temperature measurement techniques. The effect of an LED lens on junction temperature and optical extraction was investigated by examining the change in the thermal and optical properties of an LED chip after the LED lens was removed. In addition, the results of the green LED were compared with a 450-nm blue LED and verified with numerical findings. As a result, it has been determined that the thermal behavior of LEDs is significantly affected by electrical conditions, since the junction temperature of green and blue LEDs has risen by around 45% after the operating current has been increased from 200 to 500 mA.