Improvement of ultra-high-brightness white LEDs

Tanja Mesli
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引用次数: 8

Abstract

As LEDs became the preferred light source for coloured light, the focus is now on improving the performance of white LEDs, to achieve the required levels for applications such as general lighting. One especially interesting automotive application of white LEDs are daytime running lights, which may become mandatory in the near future in Europe. In this application the specific advantages of LEDs like long lifetime, high efficiency, robustness and freedom for the designers can be fully employed. The most common way to realize a white LED is the approach of a luminescence conversion LED, where blue light of a GaN Chip is partly transformed into yellow light by a phosphor. The combination of the not converted blue and the yellow light results in white light. A strong increase of the luminous flux becomes possible by the use of High Power LED Chips, high efficient yellow phosphors and a packaging that offers an excellent thermal management. First of all, the application of a High Power LED Chip allows an increase of the electrical current up to 1 Ampere. While this increases the light output significantly, the thermal management of the LED package has to be improved in order to remove the heat created by the LED chip. Apart from chip efficiency and driving current the brightness of a white LED also strongly depends on the efficiency of the used phosphor. Today's typically used phosphors are for example YAG:CE, or with Europium 2+ doped compounds. The required quantum efficiency should be higher than 90% for good results in the luminous efficiency. Furthermore, for certain applications such as automotive front lighting the converter even has to be stable under temperature conditions up to 120°C, be resistant to humidity and guarantee a long lifetime. In this contribution we will present a comparison of several different types of phosphors with emphasis on their temperature dependent behaviour.
超高亮度白光led的改进
随着led成为彩色光的首选光源,现在的重点是提高白光led的性能,以达到一般照明等应用所需的水平。白光led的一个特别有趣的汽车应用是日间行车灯,这可能在不久的将来在欧洲成为强制性的。在这种应用中,led的特定优势,如长寿命、高效率、坚固性和设计人员的自由可以充分利用。实现白光LED最常见的方法是发光转换LED的方法,其中氮化镓芯片的蓝光部分被荧光粉转化为黄光。未转换的蓝光和黄光结合在一起就产生了白光。通过使用高功率LED芯片,高效黄色荧光粉和提供出色热管理的封装,光通量的大幅增加成为可能。首先,高功率LED芯片的应用允许电流增加到1安培。虽然这大大增加了光输出,但为了消除LED芯片产生的热量,LED封装的热管理必须得到改进。除了芯片效率和驱动电流外,白光LED的亮度也很大程度上取决于所用荧光粉的效率。今天通常使用的荧光粉例如YAG:CE,或与铕2+掺杂的化合物。要想获得良好的发光效率,所要求的量子效率应高于90%。此外,对于某些应用,如汽车前照灯,转换器甚至必须在高达120°C的温度条件下保持稳定,耐湿度并保证长寿命。在这篇文章中,我们将介绍几种不同类型的荧光粉的比较,重点是它们的温度依赖行为。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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