Purpose

Optimization of light-emitting diodes’ (LEDs’) design together with long-term reliability is directly correlated with their photometric, electric and thermal characteristics. For a given thermal layout of the LED system, the maximum luminous flux occurs at an optimal electrical input power and can be determined using a photo-electro-thermal (PET) theory. The purpose of this study is to extend the application of the luminous flux equation in PET theory for low-power (LP) LEDs.

Design/methodology/approach

LP surface-mounted device LEDs were mounted on substrates of different thermal resistances. Three LEDs were attached to substrates which were flame-retardant fiberglass epoxy (FR4) and two aluminum-based metal core printed circuit boards (MCPCBs) with thermal conductivities of about 1.0 W/m.K, 2.0 W/m.K and 5.0 W/m.K, respectively. The conjunction of thermal transient tester and thermal and radiometric characterization of LEDs system was used to measure the thermal and optical parameters of the LEDs at a certain range of input current and temperature.

Findings

The validation of the extended application of the luminous flux equation was confirmed via a good agreement between the practical and theoretical results. The outcomes show that the optimum luminous flux is 25.51, 31.91 and 37.01 lm for the LEDs on the FR4 and the two MCPCBs, respectively. Accordingly, the stipulated maximum electrical input power in the LED datasheet (0.185 W) is shifted to 0.6284, 0.6963 and 0.8838 W between the three substrates.

Originality/value

Using a large number of LP LEDs is preferred than high-power (HP) LEDs for the same system power to augment the heat transfer and provide a higher luminous flux. The PET theory equations have been applied to HP LEDs using heatsinks with various thermal resistances. In this work, the PET theory luminous flux equation was extended to be used for Indium Gallium Aluminum Phosphide LP LEDs attached to the substrates with dissimilar thermal resistances.

中文翻译：

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使用具有不同热阻的基板增强基于InGaAlP的低功率SMD LED的光通量

目的

发光二极管（LED）设计的优化以及长期的可靠性与它们的光度，电和热特性直接相关。对于给定的LED系统热布局，最大光通量出现在最佳电输入功率下，并且可以使用光电热（PET）理论确定。这项研究的目的是扩大光通量方程在低功率（LP）LED的PET理论中的应用。

设计/方法/方法

LP表面安装的设备LED安装在具有不同热阻的基板上。将三个LED附着到分别为阻燃性玻璃纤维环氧树脂（FR4）和两个铝基金属芯印刷电路板（MCPCB）的基板上，导热率分别约为1.0 W / mK，2.0 W / mK和5.0 W / mK。 。将热瞬态测试仪与LED系统的热和辐射特性结合起来，用于在一定范围的输入电流和温度下测量LED的热和光学参数。

发现

通过实际和理论结果之间的良好一致性，证实了光通量方程的扩展应用的有效性。结果表明，FR4和两个MCPCB上的LED的最佳光通量分别为25.51、31.91和37.01 lm。因此，LED数据表中规定的最大电输入功率（0.185 W）在三个基板之间转移到0.6284、0.6963和0.8838W。

创意/价值

对于相同的系统功率，使用大量的LP LED比高功率（HP）LED更可取，以增加热量传递并提供更高的光通量。PET理论方程已应用于具有各种热阻的散热器的HP LED。在这项工作中，扩展了PET理论光通量方程，以用于附着到具有不同热阻的基板上的铟镓铝磷化LP LED。