Energy and the environment are major tests for humans in the 21st century, so green energy conservation has become the focus of the world. Taking lighting as an example, its power consumption accounts for about 20% of the total, which greatly reduces lighting power consumption as an important way to save energy. With its energy-efficient features, LEDs have never seen an unprecedented opportunity in the field of lighting.
LED light-emitting diodes, also known as Light Emitting Diodes (LEDs), are semiconductor light-emitting devices that convert electrical energy into light energy and are solid-state light sources. It uses a solid semiconductor chip as a light-emitting material. When a forward voltage is applied to both ends, carriers in the semiconductor recombine, releasing excess energy and causing photon emission to generate visible light. Compared with conventional vacuum incandescent bulbs, semiconductor LED light sources have unparalleled advantages. The working life of semiconductor LED is extremely long, more than 10 times that of traditional lighting equipment, which effectively reduces the cost; it has low power consumption, high luminous efficiency and energy saving, and is a suitable candidate for future energy strategy; LED light source is small in size and weight Light and adaptable, it provides great flexibility for design and application; since white light high-power LED light source is a solid bulb, it does not need to be packaged in vacuum glass, so it is resistant to impact and collision; LED light source is still a pollution-free Mercury source.
Especially in recent years, with the improvement of LED chip technology, the reduction of price and the maturity of related drive circuits, the application of LED light source in the field of illumination has become possible. In the current global energy shortage, some developed countries and regions in the world have implemented plans to promote the development of the LED industry. The United States, Japan and other countries and Taiwan have predicted the LED lighting efficiency. 55% of the US incandescent lamps and fluorescent lamps have been replaced by LEDs, saving 35 billion US dollars in electricity bills per year and reducing 725 million tons of carbon dioxide emissions per year. The replacement of 100% of incandescent lamps in Japan with LEDs can reduce the power generation of 1-2 nuclear power plants and save more than 1 billion liters of crude oil per year. In Taiwan, 25% of incandescent lamps and 100% fluorescent lamps are replaced by LEDs, saving 11 billion kWh per year.
The world-famous 2008 Beijing Olympic Games and the 2010 Shanghai World Expo are all around the same theme of green energy conservation, which has brought huge historical opportunities to the development of China's LED lighting industry. According to the well-known domestic research company Sinotes (Sinotes) According to the forecast released by the Olympics and the Expo, the scale of China's LED lighting market will grow rapidly from 4.85 billion yuan in 2007 to 9.81 billion yuan in 2010. In the context of global energy shortages and increasing environmental protection requirements, LED lighting technology has significant advantages such as high brightness, long service life, energy saving, and environmental protection. With the rapid development of LED technology, LEDs have become the common lighting source. Getting closer and closer will surely become a new lighting revolution in the history of human lighting following incandescent and fluorescent lamps.
However, in place of traditional incandescent lamps, high-brightness white LEDs still have problems of poor heat dissipation and low light extraction rate, because heat dissipation directly affects the reliability of LEDs, which in turn affects their life and applications, while low light output directly limits LEDs. The development of LED thermal dissipation and packaging optical design is particularly important. The key to improving the light extraction rate is the selection and application of potting glue and phosphor. Except for some of the heat from the LED chip, the energy released by the phosphor after the radiation will enter the potting glue, for the current high power white light. LEDs, because of the good thermal stability and optical characteristics of silica gel, are the world's major LED manufacturing businesses, such as Nichia Chemical of Japan. Germany's OSRAM, the United States' CREE, the Netherlands's Philips, the United States' GE, etc. are all packaged with two-component transparent silica gel as potting compound. However, although silica gel has good thermal stability, its thermal conductivity is extremely low, so a large amount of heat will accumulate in the silica gel material and cause the material to age. The failure of a large number of reported LED lighting products is related to silica gel. So far, due to the unknown mechanism of aging of silica gel and the relationship between its molecular structure and optical characteristics, due to the uncertainty of materials, the world's major LED lighting companies cannot be in their product description. Accurate prediction of LED lifetime also delays the true popularity of LED products.
Recently, the author was informed that Dr. Cai Dengke (Dortmund University of Technology, Germany), was invited by the internationally renowned journal of Journal of Molecular Structure to publish an article: Raman, mid-infrared, near-infrared and ultra-viovio-visiblespectroscopy of PDMSsiliconerubberfor characterization of polymeropticalwaveguidematerials, in which he analyzed in detail The relationship between the molecular structure of silica gel and optical absorption, the spectrum from ultraviolet to infrared. Moreover, he described in detail the absorption spectrum of silica gel in the visible range, and accurately analyzed and summarized the absorption peaks in this range, including its intensity. These data will play a vital role in the analysis of LED aging. At present, the use of spectroscopy to analyze organic matter aging is a very common test method. With the data summarized by Dr. Cai, researchers can accurately determine the cause from the molecular structure. This leads to the failure of the silica gel, and then the silicone material company can be further evaluated to further improve the reliability of the corresponding silica gel molecule.
In addition, due to the great differences in the mechanical properties of silica gel and LED chips, the high temperature in the silicone material will cause it to self-peel and ultimately affect the light extraction rate from the LED chip. In the understanding of Dr. Cai's research results, we found that Dr. Cai has also analyzed and summarized this problem. Through the analysis of silica gel polymerization, through mechanical tests and aging tests, he concluded that it can be widely used. Adhesive formulations for a variety of substrates, and this material can be applied to a variety of substrates by simple spraying or spin coating, making it ideal for LED packages. This research result has also been published by the internationally renowned magazine MicrofluidicandNanofluidic.
LED packaging involves knowledge of light, heat, electricity, polymer materials, etc. It is a comprehensive and complex subject. Packaging materials, silica gel, etc. have always been the main factors affecting LED quality and life. Technical Improvement. We believe that with Dr. Cai's research results, LEDs are not far from true indoor lighting.
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