Decay Mechanisms of Radiation Pattern and Optical Spectrum of High-Power LED Modules in Aging Test

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Decay of radiation pattern and optical spectrum of high-power LED modules fabricated by different manufacturers after a thermal-aging test were investigated experimentally and numerically. Samples were aged at <formula formulatype="inline"><tex Notation="TeX">${65}\,{^\circ}$</tex> </formula>C, <formula formulatype="inline"><tex Notation="TeX">${85}\,{^\circ}$</tex></formula>C, and <formula formulatype="inline"> <tex Notation="TeX">${95}\,{^\circ}$</tex></formula>C under a constant current of 350 mA. The results showed that the radiation pattern of the LED modules at the two view angles of <formula formulatype="inline"><tex Notation="TeX">$\pm$</tex></formula>(45 <formula formulatype="inline"><tex Notation="TeX">$\,{^\circ} {\sim} {75}\,{^\circ}$</tex></formula>) decreased more than the other angles as aging time increased. This was due to the reduction of optical power from corner shape of lens. Due to the degradation of lens material after thermal aging, the center wavelength of the LED spectrum shifted 5 nm. Furthermore, the radius curvature of plastic lens was observed to have 6–<formula formulatype="inline"><tex Notation="TeX">$\hbox{70}\, {\mu}$</tex></formula>m contraction as aging times increased. The key module package related to the decrease of power density, the change of radiation pattern, and the shift of optical spectrum in high-power LED modules under thermal aging were due to the degradation of lens material and lens structure. Both experimental and simulated results clearly indicated that improving the lens structure and lens material is essential to extend the operating life of the high-power LED modules. This study may provide practical LED package guidelines in low-cost consumer applications. </para>