Application of LED light source in lighting field

  The application of LED light sources in the field of lighting is a product of the rapid development of semiconductor luminescent material technology and the gradual penetration of the concept of "green lighting". "Green lighting" is a new concept that was not proposed in the field of foreign lighting in the 1980s. The implementation of my country's "green lighting project" began in 1996. An important step to realize this plan is to develop and promote high-efficiency, energy-saving lighting fixtures, save lighting power, reduce environmental and light pollution, and establish a high-quality, efficient, economical, comfortable, safe, reliable, and environmentally friendly lighting system

A concept of LED lighting LED (LightEmittingDiode), also known as light-emitting diodes, they use solid semiconductor chips as luminescent materials, when a forward voltage is applied to both ends, the carriers in the semiconductor recombine and release excess energy to cause photon emission Visible light.

(1) The development history of LEDs The use of semiconductor PN junction light-emitting source principles to make LEDs came out in the early 1960s. In 1964, red light-emitting diodes first appeared, followed by $LEDs. It was not until 1994 that blue and green LEDs were successfully developed. In 1996, the white LED was successfully developed by the Japanese company Nichia (Nichia). With its inherent characteristics, such as power saving, long life, vibration resistance, fast response speed, cold light source, etc., LEDs are widely used in indicator lights, signal lights, display screens, landscape lighting and other fields, which can be seen everywhere in our daily lives. , Household appliances, telephones, instrument panel lighting, automobile anti-fog lights, traffic lights, etc. However, due to its poor brightness and high price, it cannot be popularized and applied as a general-purpose light source. In recent years, with the continuous deepening of research on semiconductor light-emitting materials, the continuous progress of LED manufacturing technology and the development and application of new materials (nitride crystals and phosphors), breakthroughs have been made in ultra-high-brightness LEDs of various colors. Its luminous efficiency has increased by nearly 1,000 times, and all colors in the visible light band have been realized in terms of chromaticity. The most important of which is the emergence of ultra-high brightness white LEDs, which makes it possible for the LED application field to leap over to the high-efficiency lighting source market. Someone once pointed out that high-brightness LED will be one of the greatest inventions of mankind since Edison invented the incandescent light bulb.

(2) LED light-emitting principle Light-emitting diodes are mainly composed of PN junction chips, electrodes and optical systems. The luminous body-chip area is 10.12mil (1mil=0.0254 square millimeter). At present, large-chip LEDs appear internationally, with a chip area of 40mil. The light-emitting process includes three parts: carrier injection under forward bias, recombination radiation and light energy transmission. The tiny semiconductor chip is encapsulated in a clean epoxy resin. When electrons pass through the chip, 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 the electron and the hole, the higher the energy of the photon produced. The energy of photons in turn corresponds to the color of light. In the spectrum of visible light, 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, most commercially available white light LEDs are two-wavelength, that is, a blue single chip and YAG$ phosphor are mixed to produce white light. In the future, three-wavelength white LEDs are more promising, that is, inorganic ultraviolet chips are mixed with red, blue, and green phosphors to produce 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, the luminous efficiency of LED has been greatly improved. The lighting effect of incandescent lamps and halogen tungsten lamps is 12-24 lumens/W, fluorescent lamps 50-70 lumens/W, sodium lamps 90-140 lumens/W, 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, countries all over the world are stepping up research on improving the luminous efficiency of LEDs, and their luminous efficiency will be greatly 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 1.5~3.5V, 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 that of incandescent bulbs and one-half that of fluorescent tubes. Japan estimates that if LEDs with light efficiency twice as high as fluorescent lamps are used to replace half of Japanese incandescent lamps and Fluorescent lights. The equivalent of 6 billion liters of crude oil can be saved every year. For the bridge guardrail light example, 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 changed in colorful colors.

3. Long service life. The use of electronic light field radiation luminescence, filament luminescence is easy to burn, thermal deposition, light attenuation and other shortcomings. The LED lamp is small in size, light in weight, epoxy resin encapsulated, can withstand high-strength mechanical shock and vibration, and is not easy to break. 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, the light color is soft, no glare; it does not contain mercury, sodium, etc. that may harm 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 a solid luminous body, which is shock-resistant, impact-resistant and not easily broken. The 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 and small lighting product, and it is also easy to install and maintain. Of course, energy saving is the main reason why we consider using LED light sources. Perhaps LED light sources are more expensive than traditional light sources, but one year of energy saving can recoup the investment in the light source, so as to obtain a net income period of several times each year in 4-9 years. .

Second, the application prospects and trends of LED lighting source technology For a long time, due to the low light efficiency of LEDs, its applications are mainly concentrated in various display fields. With the emergence of ultra-high-brightness LEDs (especially white LEDs), applications in the lighting field become possible. According to forecasts by international authoritative organizations, the 21st century will enter the era of new lighting sources represented by LEDs, which are called the fourth generation of new light sources.

(1) Prospects and development trends At present, lighting consumption accounts for about 20% of the entire power consumption. Significantly reducing lighting power consumption is an important way to save energy. In order to achieve this goal, the industry has researched and developed many energy-saving lighting appliances, and A certain effect has been achieved. However, the requirements for "green lighting" are far from enough, and it is imperative to develop and apply more efficient, reliable, safe, and durable new light sources. LED is attracting the world's attention with its inherent superiority. The United States, Japan and other countries and Taiwan have predicted the benefits of LED lighting. 55% of incandescent lamps and 55% of fluorescent lamps in the United States are replaced by LEDs, saving US$35 billion in electricity bills each year and reducing 755 million tons of carbon dioxide emissions each year. Replacing 100% of incandescent lamps in Japan with LEDs can reduce the power generation of 1 to 2 nuclear power plants and save more than 1 billion liters of crude oil consumption every year. In Taiwan, 25% of incandescent lamps and 100% of fluorescent lamps are replaced by white LEDs, saving 11 billion kilowatt-hours of electricity each year. Japan compiled the "21st Century Plan" as early as 1998 to conduct practical research on LED light sources for lighting in the new century. In recent years, Nichia Chemical, Toyoda Gosei, SONY, and Jiayou Electric have all launched LED lighting products. World-renowned lighting companies such as Philips, Osram, GE, etc. have also invested a lot of manpower and material resources in the research, development and production of LED lighting products. The United States GE and EMCORE have established a new company to develop white LEDs to replace incandescent lamps, compact fluorescent lamps, tungsten halogen lamps and automotive lamps. Germany’s Osram and Siemens cooperated to develop LED lighting systems. Taiwan’s current LED output is second only to Japan before the United States. Since 1998, Taiwan has invested 600 million Taiwan dollars in related development work. The development history of LED has been decades, but the application in the field of lighting is still new technology. With the rapid development of LED technology and the gradual improvement of its luminous efficiency, the application market of LEDs will become more extensive. Especially in the context of rising global energy shortage concerns, the prospects of LEDs in the lighting market have attracted global attention. The industry believes that becoming the most promising market and the largest market in the next 10 years will also be the most promising commodity to replace incandescent lamps, tungsten lamps and fluorescent lamps.

(2) The main technical problems in lighting applications. In recent years, the luminous efficiency of LEDs is gradually improving, and commercial 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 increasing steadily. 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 LEDs as the lighting source must be able to emit more light and must have higher energy efficiency. Second, there is still a certain gap between the light emitted by the LED and the natural light. Incandescent lamps have a very strong light component, giving people a warm feeling. The white light emitted by the white LED has a blue light component. Under the illumination of this light, people's vision is not very natural. The third is higher prices. This is the main reason that affects the popularity of LED lighting. However, due to the improvement of chip technology in recent years, manufacturing costs are falling sharply. In the past three years, the price of LEDs has dropped by nearly 50%. It is moving towards high efficiency and low cost. This is the application of LEDs in the field of lighting. Provides favorable conditions. In addition, a better price-performance ratio can also make up for the lack of cost price.

3. Application of LED lighting technology in lighting environment. Because LED light source has the characteristics of high luminous efficiency, low power consumption, long service life, strong safety and reliability, and is conducive to environmental protection, it has been widely used in urban lighting environment in recent years. Applications. At present, it has been used in digital symphony, guardrail lighting, square lighting, courtyard lighting, projection lighting, underwater lighting series. Many cities use LED light source lighting technology in the construction of urban lighting environment, 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 Yan'an Road Lighting Project, Hunan Changde City Danyang Flyover, Nantong Communication Tower Lighting engineering, etc.

With the further development of national urbanization, the field of lighting environment (including street lights, landscape lights, artistic lights, etc.) construction 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 applied in the field of urban landscape lamp construction. However, 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 steps are needed. The research and discussion of the LED light source to solve the technical problems existing in the lighting application of the LED light source, it is also necessary for the LED light source manufacturer 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 can be used in Play a greater role in urban lighting construction.