The application of LED light sources in the field of lighting is a product of the rapid development of semiconductor light-emitting materials technology and the concept of "green lighting" gradually gaining popularity. "Green lighting" is a new concept that was not proposed in the field of foreign lighting in the 1980s. The implementation of the "green lighting project" in China began in 1996. An important step to realize this plan is to develop and promote efficient and energy-saving lighting appliances, save lighting power, reduce the environment and light pollution, and establish a high-quality, efficient, economical and comfortable, safe, reliable, and environmentally friendly lighting system
1. LED lighting concept LED (LightEmitTIngDiode), also known as light-emitting diodes, they use solid semiconductor chips as luminescent materials. When a forward voltage is applied at both ends, the carriers in the semiconductor recombine, releasing excess energy and causing photon emission. Produces visible light.
(1) The history of LED development The application of the principle of semiconductor PN junction light source made LED came out in the early 1960s. In 1964, red light-emitting diodes first appeared, and then yellow LEDs appeared. It was not until 1994 that blue and green LEDs were successfully developed. In 1996, white LED was successfully developed by Nichia Corporation (Japan). LEDs are widely used in indicator lights, signal lights, display screens, landscape lighting and other fields due to their inherent characteristics, such as power saving, long life, vibration resistance, fast response, cold light source, etc., which are everywhere in our daily life , Household appliances, telephones, instrument panel lighting, automobile anti-fog lights, traffic lights, etc. However, due to the limitations of poor brightness and high price, it cannot be used as a general light source. In recent years, with the continuous deepening of research on semiconductor luminescent materials, the continuous advancement of LED manufacturing processes and the development and application of new materials (nitride crystals and phosphors), ultra-high brightness LEDs of various colors have made breakthrough progress The luminous efficiency has been improved by nearly 1,000 times, and all colors in the visible light band have been realized in chromaticity. The most important thing is the emergence of ultra-high-brightness white LEDs, which makes it possible for LED applications to span the high-efficiency lighting source market. It has been pointed out that high-brightness LEDs will be one of the greatest inventions of mankind after Edison invented incandescent light bulbs.
(B) LED light-emitting principle Light-emitting diodes are mainly composed of PN junction chips, electrodes and optical systems. The area of the luminous body-wafer is 10.12mil (1mil = 0.0254mm2). At present, large-chip LEDs have appeared in the world, with a wafer area of 40mil. The luminescence process consists of three parts: carrier injection under forward bias, recombination radiation and light energy transmission. The tiny semiconductor wafer is encapsulated in a clean epoxy resin. When electrons pass through the wafer, the negatively charged electrons move to the positively charged hole area and recombine with it. The electrons and holes disappear while generating photons. The greater the energy (band gap) between electrons and holes, the higher the energy of the photons produced. The energy of the photon in turn corresponds to the color of the light. In the visible light spectrum, blue light and purple light carry the most energy, and orange light and red light carry the least energy. Because different materials have different band gaps, they can emit different colors of light. The mainstream of LED lighting sources will be high-brightness white LEDs. At present, the white light LEDs that have been commercialized are mostly two wavelengths, that is, a blue single crystal chip plus YAG yellow phosphor powder is mixed to generate white light. In the future, three-wavelength white LEDs are more promising, that is, inorganic ultraviolet chips plus red, blue, and green phosphors are used to generate white light. It will replace fluorescent lamps, compact energy-saving fluorescent bulbs, and LED backlights.
(3) Basic characteristics of LED light source
1. High luminous efficiency After decades of technological improvement, LED has greatly improved its luminous efficiency. Incandescent and tungsten halogen lamps are 12-24 lumens / watt, fluorescent lamps 50-70 lumens / watt, sodium lamps 90-140 lumens / watt, most of the power consumption becomes heat loss. The improved LED light efficiency will reach 50-200 lumens / watt, and its light monochromaticity is good, the spectrum is narrow, and it can directly emit colored visible light without filtering. At present, all countries in the world are stepping up their efforts to improve LED light efficiency, and their luminous efficiency will be further improved in the near future.
2. Low power consumption LED single tube power 0.03 ~ 0.06 watts, using DC drive, single tube driving voltage 1.5 ~ 3.5 volts, current 15 ~ 18 mA, fast response speed, can be operated at high frequency. In the case of the same lighting effect, the power consumption is one ten thousandth of incandescent light bulbs, one half of fluorescent tubes, Japan estimates that if LEDs with light efficiency two times higher than fluorescent lamps are used to replace half of Japan ’s incandescent lamps and Fluorescent light. It can save 6 billion liters of crude oil every year. In the case of bridge guardrail lights, a fluorescent lamp with the same effect is more than 40 watts, while the power of each LED is only 8 watts, and it can be colorfully changed.
3. Long service life. It adopts the electronic light field to emit light, and the filament is easy to burn, thermal deposition, light attenuation and other shortcomings. The LED lamp is small in size, light in weight, and encapsulated in epoxy resin, which can withstand high-strength mechanical shock and vibration and is not easily broken. The average life span is 100,000 hours. The service life of LED lamps can reach 5 to 10 years, which can greatly reduce the maintenance cost of lamps and avoid the pain of frequent lamp replacement.
4. Strong safety and reliability, low heat generation, no heat radiation, cold light source, safe to touch: can accurately control the light type and luminous angle, soft color, no glare; does not contain mercury, sodium and other elements that may endanger health substance. The built-in micro-processing system can control the luminous intensity, adjust the luminous mode, and realize the combination of light and art.
5. It is conducive to environmental protection. The LED is an all-solid luminous body. It is shock-resistant and shock-resistant and is not easily broken. Waste can be recycled and there is no pollution. The light source is small in size and can be combined at will. It is easy to develop into a light, thin, short and small lighting product, which is also easy to install and maintain. Of course, energy saving is the most important reason for us to consider using LED light sources. Perhaps LED light sources are more expensive than traditional light sources, but the investment in light sources is recovered with one year of energy saving, thereby obtaining a net energy saving period of several times per year in 4-9 years .
Second, the application prospects and trends of LED lighting source technology for a long time, due to the low efficiency of LED light, its application is mainly concentrated in various display fields. With the emergence of ultra-high brightness LEDs (especially white LEDs), applications in the field of lighting become possible. According to the predictions of international authoritative organizations, the 21st century will enter the era of new lighting sources represented by LEDs, known as the fourth generation of new light sources.
(I) Prospects and development trends At present, lighting consumption accounts for about 20% of the entire power consumption, and greatly reducing lighting power consumption is an important way to save energy. To achieve this goal, the industry has researched and developed many kinds of energy-saving lighting appliances, and A certain effect has been achieved. However, the requirements of "green lighting" are far from enough, and the development and application of more efficient, reliable, safe, and durable new light sources is imperative. LED is attracting the world's attention with its inherent superiority. The United States, Japan and other countries and Taiwan have predicted the effectiveness of LED lighting. 55% of incandescent lamps and 55% of fluorescent lamps in the United States have been replaced by LEDs, saving $ 35 billion in electricity bills each year and reducing 755 million tons of carbon dioxide emissions each year. The replacement of 100% of incandescent lamps in Japan with LEDs can reduce the power generation of 1 or 2 nuclear power plants and save more than 1 billion liters of crude oil consumption each year. In Taiwan, 25% of incandescent lamps and 100% of fluorescent lamps are replaced by white LEDs, saving 11 billion kWh of electricity each year. As early as 1998, Japan compiled the "21st Century Plan" to conduct practical research on LED light sources for lighting in the new century. In recent years, Japan's Nichia Chemical, Toyota Synthetic, SONY, Jiayou Electric, etc. have all come out with LED lighting products. World-renowned lighting companies such as Philips, Osram, GE, etc. have also invested a lot of manpower and resources in the research, development and production of LED lighting products. American GE and EMCORE cooperated to set up a new company, specializing in the development of white LEDs, to replace incandescent lamps, compact fluorescent lamps, tungsten halogen lamps and automotive lamps. The German company Osram cooperates with Siemens to develop LED lighting systems. Taiwan ’s current LED production is second only to Japan before it is listed in the United States. Since 1998, it has invested NT $ 600 million in related development work. LED has a history of development for decades, but its application in the field of lighting is still a new technology. With the rapid development of LED technology and the gradual improvement of its luminous efficiency, the application market of LED will be more extensive. Especially in the context of the rising concern of global energy shortage, the prospect of LED in the lighting market has attracted more global attention. The industry believes that it will become the most promising market and the largest market in the next 10 years, and it will also be the largest potential commodity to replace incandescent lamps, tungsten filament lamps and fluorescent lamps.
(B) The main technical problems in lighting applications In recent years, the luminous efficiency of LEDs is gradually improving, and the commercialized devices have reached the level of incandescent lamps. The luminous efficiency of white LEDs used in landscape lamps is close to the level of fluorescent lamps, and is steadily increasing. in. However, there are still some technical problems in the popularization and application of lighting: First, the luminous flux needs to be further improved. Using LED as the lighting source must emit more light and must have higher energy efficiency. Second, there is still a certain gap between the light emitted by the LED and natural light. The incandescent lamp has a very strong yellow light composition, giving a warm feeling. The white light emitted by the white light LED has a component of blue light. Under this light, people's vision is not very natural. The third is higher prices. This is the main reason affecting the popularity of LED lighting. However, in recent years, due to the improvement of wafer technology, the manufacturing cost is falling sharply. In the past three years, the price of LED has dropped by nearly 50%. It is developing in the direction of high efficiency and low cost. Provided favorable conditions. In addition, a better price-performance ratio can also make up for deficiencies in cost and price.
Third, the application of LED lighting technology in the light environment Because the LED light source has the characteristics of high luminous efficiency, low power consumption, long service life, strong safety and reliability, and is beneficial to environmental protection, it has been widely used in urban lighting environments in recent years Applications. It has been used in digital Symphony, guardrail lighting, square lighting, courtyard lighting, floodlighting, underwater lighting series. Many cities use LED light source lighting technology in urban lighting environment construction, which has produced good results and accumulated rich experience. Such as Guangzhou Electric Power Building, Guangzhou Hedong Bridge, Guangzhou Industrial and Commercial Bank Building, Zhuhai Yingbin South Road Lighting Project, Dongguan Central City Lighting Project, Zhengzhou Henan Medical University Overpass, Shanghai Yanan Road Lighting Project, Hunan Changde Danyang Overpass, Nantong Communication Tower Lighting engineering, etc.
With the further development of urbanization throughout the country, the construction of lighting environment (including street lights, landscape lights, art lights, etc.) will continue to expand, and the application of LED light sources will also continue to develop. As the fourth-generation new light source, LED has been effectively used in the construction of urban landscape lights, but to replace high-power high-pressure sodium lamps, high-pressure mercury lamps, metal halide lamps and other light sources in the construction and maintenance of street lamps, further needs Research and discussion to seriously solve the technical problems of LED light sources in lighting applications, and LED light source manufacturers need to combine the actual situation of the street light industry to produce new products that meet the needs of street light construction and maintenance, so that the fourth generation of new light sources Play a greater role in the construction of urban lighting.
