System for measuring the junction temperature of a light emitting diode immersed in liquid nitrogen

A versatile system has been developed for the measurement under LABVIEW™ control of junction temperatures in a light emitting diode (LED). Measurements are reported on a commercially available high-intensity InGaAlP LED immersed in liquid nitrogen and driven by currents in the range of $18.5–204mA$⁠. The measured junction temperature has an expanded uncertainty of $±2K$ at the 95% level of confidence for temperatures from $70to298K$⁠. Using the measured junction temperatures, the junction-to-case thermal resistance of the LED was established as $440K∕W$ for devices with intact encapsulation and $307K∕W$ for partial encapsulation.