Application of LED light sources in the lighting field

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

1. LED lighting concept LED (Light Emitting Diode), also known as light-emitting diode, uses solid semiconductor chips as light-emitting materials. When a forward voltage is applied to both ends, the carriers in the semiconductor recombine and release excess energy to cause photon emission to produce visible light.

(I) The development history of LED LEDs are made using the principle of semiconductor PN junction light source. They came out in the early 1960s. In 1964, red light-emitting diodes first appeared, followed by yellow LEDs. It was not until 1994 that blue and green LEDs were successfully developed. In 1996, Nichia Corporation of Japan successfully developed white LEDs. 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 speed, and cold light source. They can be seen everywhere in our daily lives, such as household appliances, telephones, dashboard lighting, car fog lights, traffic lights, etc. However, due to the limitations of poor brightness and high prices, they cannot be promoted and applied as general light sources. In recent years, with the continuous deepening of research on semiconductor luminescent materials, the continuous advancement of LED manufacturing technology and the development and application of new materials (nitride crystals and phosphors), ultra-high brightness LEDs of various colors have made breakthrough progress, and their luminous efficiency has increased by nearly 1,000 times. In terms of chromaticity, all colors in the visible light band have been achieved. The most important of these is the emergence of ultra-high brightness white light LEDs, which makes it possible for LED applications to cross over to 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 the incandescent light bulb.

(II) LED light-emitting principle The light-emitting diode is mainly composed of a PN junction chip, an electrode and an optical system. The area of ​​its luminous body, the chip, is 10.12mil (1mil=0.0254 square millimeters). At present, large chip LEDs have appeared in the world, and the chip area is as high as 40mil. Its 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 and photons are generated at the same time. The greater the energy (band gap) between electrons and holes, the higher the energy of the generated photons. The energy of photons in turn corresponds to the color of light. In the visible light spectrum, blue light and purple light carry the most energy, while orange light and red light carry the least energy. Because different materials have different band gaps, they can emit light of different colors. The mainstream of LED lighting sources will be high-brightness white light LEDs. At present, most of the commercialized white light LEDs are two-wavelength, that is, blue light single chip plus YAG yellow phosphor mixed to produce white light. The most promising future is the three-wavelength white light LED, which produces white light by mixing inorganic ultraviolet light chips with red, blue and green phosphors. It will replace the fluorescent lamps, compact energy-saving fluorescent bulbs and LED backlight sources.

(III) Basic characteristics of LED light sources

1. High luminous efficiency After decades of technological improvements, the luminous efficiency of LED has been greatly improved. Incandescent lamps and halogen tungsten lamps have a luminous efficiency of 12-24 lumens/watt, fluorescent lamps have a luminous efficiency of 50-70 lumens/watt, and sodium lamps have a luminous efficiency of 90-140 lumens/watt. Most of the power consumption is converted into heat loss. After improvement, the luminous efficiency of LED will reach 50-200 lumens/watt, and its light has good monochromaticity and a narrow spectrum. It can directly emit colored visible light without filtering. At present, countries around the world are stepping up research on improving LED luminous efficiency. In the near future, its luminous efficiency will be further improved.

2. Low power consumption. The power of a single LED tube is 0.03-0.06 watts. It uses DC drive, and the single tube drive voltage is 1.5-3.5 volts, the current is 15-18 mA, the response speed is fast, and it can operate at high frequencies. Under the same lighting effect, the power consumption is one ten-thousandth of an incandescent bulb and one-half of a fluorescent tube. Japan estimates that if LEDs with twice the light efficiency of fluorescent lamps are used to replace half of Japan's incandescent and fluorescent lamps, it can save the equivalent of 6 billion liters of crude oil each year. For example, for bridge guardrail lights, a fluorescent lamp with the same effect consumes more than 40 watts, while the power of each LED is only 8 watts, and it can change in seven colors.

3. Long service life. The use of electronic light field radiation luminescence has the disadvantages of easy burning of filament luminescence, heat deposition, and light attenuation. However, LED lamps are small in size, light in weight, and epoxy resin encapsulated. They can withstand high-intensity mechanical shock and vibration and are not easy to break. The average life span is 100,000 hours. The service life of LED lamps can reach 5-10 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 light angle, soft light color, no glare; does not contain mercury, sodium and other substances that may endanger health. The built-in microprocessor system can control the luminous intensity, adjust the light mode, and realize the combination of light and art.

5. Environmentally friendly LED is a full solid light source, shock-resistant, impact-resistant, not easy to break, waste can be recycled, 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 short 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. LED light sources may be more expensive than traditional light sources, but the investment in the light source can be recovered with one year of energy saving, thereby obtaining a net energy saving income period of several times per year in 4 to 9 years.

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

(I) Prospects and development trends At present, lighting consumption accounts for about 20% of the total electricity consumption. Greatly reducing lighting electricity 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 achieved certain results. However, it is still far from the requirements of "green lighting". It is imperative to develop and apply new light sources that are more efficient, reliable, safe and durable. 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 have been replaced by LEDs, saving $35 billion in electricity bills and reducing 755 million tons of carbon dioxide emissions each year. If Japan replaces 100% of incandescent lamps with LEDs, it can reduce the power generation of 1 to 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 light LEDs, saving 11 billion kilowatt-hours 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 launched LED lighting products. World-renowned lighting companies such as Philips, Osram, and GE have also invested a lot of manpower and material resources in the research, development and production of LED lighting products. GE and EMCORE in the United States have jointly established a new company to specialize in the development of white light LEDs to replace incandescent lamps, compact fluorescent lamps, halogen lamps and car lamps. Osram in Germany and Siemens have cooperated to develop LED lighting systems. Taiwan's current LED production is second only to Japan and ranks ahead of the United States. Since 1998, it has invested 600 million Taiwan dollars in related development work. LED has been developed for decades, but its application in the field of lighting is still a new technology. With the rapid development of LED technology, its luminous efficiency has gradually improved, and the application market of LED will be more extensive. Especially in the context of the renewed concern about global energy shortage, the prospect of LED in the lighting market has attracted more attention from the world. It is believed by the industry to become the most promising market and the largest market in the next 10 years, and it will also be the product with the greatest potential to replace incandescent lamps, tungsten lamps and fluorescent lamps.

(II) Main technical problems in lighting applications In recent years, the luminous efficiency of LED is gradually improving, and commercialized devices have reached the level of incandescent lamps. The luminous efficiency of white LEDs used in landscape lamps is close to that of fluorescent lamps and is growing steadily. 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 a 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 LED and natural light. Incandescent lamps have a very strong yellow light component, giving people a warm feeling. The white light emitted by white light LEDs has a blue light component, and people's vision is not very natural under this light. Third, the price is relatively high. This is the main reason that affects the popularity of LED lighting. However, in recent years, due to the improvement of chip 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, which provides favorable conditions for the application of LED in the field of lighting. In addition, the better cost performance can also make up for the shortcomings in cost price.

3. Application of LED lighting technology in lighting environment Because LED light sources have high luminous efficiency, low power consumption, long service life, strong safety and reliability, and are conducive to environmental protection, they have been widely used in urban lighting environments in recent years. At present, it has been applied to digital fantasy lighting, guardrail lighting, square lighting, courtyard lighting, floodlighting, and 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 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 Interchange, Shanghai Yan'an Road Lighting Project, Hunan Changde Danyang Overpass, Nantong Communication Tower Lighting Project, etc.

With the further development of urbanization in China, the field of lighting environment (including street lights, landscape lights, art lights, etc.) construction will continue to expand, and the application of LED light sources will continue to develop. As the fourth-generation new light source, LED has been effectively applied in the field of urban landscape light construction, but in order to replace high-power high-pressure sodium lamps, high-pressure mercury lamps, metal halide lamps and other light sources in street light construction and maintenance, further research and discussion are needed to seriously solve the technical problems existing in LED light sources in lighting applications. LED light source manufacturers also 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 new light source can play a greater role in urban lighting construction.