High-speed non-invasive thermal analysis of high-power light-emitting diode arrays
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Light-emitting diodes (LEDs) are pervasive in many of today's technologies. Continued maturation of the technology coupled with interest in energy efficient lighting, green technologies, and improved lighting performance has made high-power LEDs attractive candidates for replacement of incandescent sources in general lighting applications. Although LEDs are highly efficient in comparison to many traditional sources, they require more precise thermal management for optimum performance. High-power LEDs are subjected to large heat fluxes due to the relative small size of the semiconductor die. These large heat fluxes can lead to device failure, detrimental self heating effects, reduced light output, and inefficient short and long-term operation. Thus, knowledge of thermal behavior at the die level and effective packaging solutions as well as evaluation methods for both, are critical for viable high-power LED performance and are technological obstacles. In this work, non-invasive, high-speed methods for thermal evaluation and effective thermal management of high-power diode arrays are explored. High-speed infrared thermography is employed to examine temporal-thermal behavior at the die, packaging, and system level of an array of high-power LEDs. Specifically, attention was given to: estimation of die temperature, temporal characteristics of die heating, investigation of the thermal path of the diode packaging, temporal characteristics of package heating, thermal characteristics of array behavior, and thermo-temporal characteristics of an array mounted to a heat-sink at the system level. To complement high-speed thermographic imaging, spectral data was also gathered through the aid of a spectrometer. Intensity and wavelength information was collected during power cycling. Detrimental self-heating effects that can occur within the LED that lead to degraded device performance with improper thermal management were investigated.
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