Dynamic opto-electro-thermal characterization of solid state lighting devices: measuring the power conversion efficiency at high current densities

Abstract

Solid state lighting devices with high power densities require accurate characterization, as the rise of chip temperature impacts its optical, electrical, and lifetime characteristics. A detailed experimental study is performed in order to analyze opto-electro-thermal behavior as new high-power devices like laser diodes are becoming of interest. The outline of this article was inspired by two major issues identified in previous experimental approaches. First, there is some debate in the literature about the linearity of the temperature coefficient of the forward voltage. Second, there is a limited number of experimental reports on the temperature dependence of power conversion efficiency. We have shown that prior variations are the result of a diversity in the selection of electrical parameters during thermal calibrations, as both linear and non-linear relationships for temperature coefficient of voltage can be obtained. On the other hand, it was discovered that report scarcity for temperature-dependent studies can be related to the use of passive approaches for temperature-dependent measurements. In temperature-controlled environments, short pulses with high current densities may not ensure the thermal equilibrium of the device under test due to small thermal capacitance. This issue, as well as the lengthy process of passive measurements can be addressed by implementing a dynamic measurement method presented in this study. Finally, linear power conversion efficiency trends with junction temperature are demonstrated for both blue LEDs and LDs at high current densities.

Composition and luminescence properties of highly robust green-emitting LuAG:Ce/Al 2O 3 composite phosphor ceramics for high-power solid-state lighting

“…As we all know, the operating temperature of core devices in high-power white LEDs/LDs can reach up to 200 ℃, which places high demands on the thermal performance of color converter [7][8][9][10]. Currently, the main phosphor converters used in commercial white LEDs are manufactured by mixing YAG:Ce phosphor powders and silicone resins [11,12].…”

A Critical Review on the Junction Temperature Measurement of Light Emitting Diodes

“…The arrangement of suitable thermal environments and the selection of appropriate electrical inputs are crucial steps in conducting accurate FVM measurement experiments which are discussed in [ 210 ]. During the conventional FVM calibration process, the desired “n” pulse temperature (T p,(1, 2, …, n) ) should be kept constant for several minutes to perform “m” number of pulses (P 1, 2, …, m ) with a control interval in between each pulse (to).…”

“…Even though the isothermal condition can be more accurate at temperatures near to the room temperature, heat dissipation from the oven and air motion inside the oven increases temperature fluctuations, and thermal resistance between the calibration thermocouples and T j increases. To ensure pulse current temperature is equal to the T j , an oven arrangement as configured in the EVAtherm system can be used [ 29 , 96 , 115 , 129 , 181 , 210 ] in which LEDs are placed in the middle of a thermally-controlled oven with no direct contact between the heater-embedded walls. In this configuration, several thermocouples record the air temperature and PCB to increase the speed and accuracy of the isothermal condition.…”

“…Reprinted with permission from Ref. [ 210 ]. Copyright 2022, Institute of Physics and the Physical Society.…”

Porous Ce:YAG ceramics with controllable microstructure for high‐brightness laser lighting

“…Moreover, the inherent “efficiency droop” problem of LED chips cannot be avoided. On the other hand, blue laser diodes (LDs) can maintain a stable wall plug efficiency at an ultrahigh current density of 28 kA/cm 2 and have a smaller emitting area as well as lower beam divergence, which is appreciated for luminaire designs with small size 4–7 . After more than 10 years of continuous development and improvement, the laser lighting technology based on LDs has quickly occupied a leading position in the high‐end market 8–11 .…”