2013年03月06日
White LED Road Lighting 1
LED the development so far, nearly 30-year history, has made great progress, and white LED calendar for more than ten years of rehearsals, the rapid development. LED came into being in the era of severe energy shortages, pollution, and has attracted significant attention. To ease the energy shortage, the mid-1990s, the Japanese government took the lead, following the U.S. government from the financial support of the country's technology and industry to promote the development of solid-state lighting. Our government (Ministry of Science and Technology, led by, including the Department of Energy, Economic and Trade Commission, Ministry of Information Industry, as well as local government) is also strongly supported and funded the research and development of LED and set up a National Semiconductor Industry Association advancing solid-state lighting (China termed 2010 white LED luminous efficiency can be increased to 100 lm / W for semiconductor lighting) plan, and expected , and can be used to a large number of alternative light efficiency of about 90 lm / W fluorescent lamps are widely used in the field of general lighting.
A large number of our businesses, investors, researchers and technical staff have to intervene in this situation, and the large-scale investment to develop LED R & D and production so far is estimated to have invested a total of RMB billions of dollars, in less than a decade achieved outstanding results, and the formation of large-scale industrial chain.
World especially LED white LED so emphasis on their underlying causes, this huge amount of energy consumption and the resulting energy shortages, rising prices, especially caused by the environment has become a very urgent task to make energy savings. A large part of the national energy consumption for lighting. In China and developed countries, electricity for lighting accounts for about total power generation capacity of 12 to 13%, which is a very substantial loss of energy. The light source is still used worldwide inefficient incandescent light source mainly from tapping the potential is very promising.
LED focuses many talents, brilliant achievements, some of the research department announced that they have developed LED reached 120lm / W or even 150 lm / W luminous efficiency under certain conditions. Thus most enterprises have also claimed the luminous efficiency of their product has reached 70lm / W, 90lm / W or higher, the light utilization than the radiation output of each LED optical radiation is directed, even ordinary light source alone directional reflection of the lamps lighting efficiency is higher, and therefore finds that LED is the best functional lighting source, and vigorously promoted to various areas of lighting, a few years ago has been declared the LED will largely replaced by compact fluorescent lamps in 2010, a large scale into the family lighting, and asserted that white LED is the best road illumination light source.
There is no doubt that after 20 years of development, the LED in the display area has been made entirely successful, without than with the theory and has become irreplaceable display devices. Fully display its features decorative lighting, made half of LED outstanding performance in the 2008 Olympic Games opening ceremony to shake the world. But must address the fact that greater limitations in terms of functional lighting white LED persists. China is already the world's largest LED production base and consumer market, LED application fields, but due to the restrictions of the current level of technology and performance, such devices are used for functional lighting is not to use their skills. So-called high power LED, currently on the market can find the most high-power devices, but 3W, even 10W devices in R & D to large-scale production, but for conventional lighting, especially the hundreds of watts of light sources used in road lighting single The granulocyte power err too small. White LED design a lighting project amount must be great, whether it is difficult to design or cost will be worth the wait.
Common evaluation Ⅱ LED light efficiency of LED high light efficiency and long life, and many manufacturers claim their products luminous efficiency of up to 90lm / W or higher, but these data are just some laboratory in the the test initial stage when the LED is still in the highest measured in the cold state data. The so-called 50,000 hours or 100,000 hours life just early estimate of the low-power color LED.
Its theoretical light efficiency can be estimated from the LED light-emitting mechanism. As known LED is the use of carrier recombination and light emission, all of its potential energy in the carrier recombination when transformed into light energy, its internal quantum efficiency of 100% of the purposes of this process alone. Carrier collision with the crystal lattice and the loss of energy in the medium when the composite contained the kinetic energy carried by the carrier, and the electricity is consumed to overcome the resistance of the external circuit are not converted into light. Taking into account the variety of additional energy, the actual carrier recombination within the quantum efficiency does not exceed 90%.
Photons generated when the carrier recombination, has a 50% chance for outgoing radiation, part of the 50% of the photons collide with the lattice and lattice absorption is converted into heat. Portion photon propagation in the different media at the interface will be reflected back to the original medium and is absorbed, addition, as the metal the omentum or transparent conductive film of the output window of the outer electrode also allow a portion of the photons reflected by absorption, these processes will reduce the LED quantum extraction rate, the extraction rate of 80% is located in this part of the photon quantum.
Of photons generated in the carrier recombination, a 50% chance of the incoming radiation, this part of the photons reach the underlying conductive film serves as a reflective mirror, a partially reflective converted to outward output optical photons in this section, however, the inwardly or outwardly The transmission during the collision with the crystal lattice and is partially absorbed, through different media interface will also be part of the reflected or refracted back to the original medium eventually be absorbed. Substrate mirror reflection efficiency and the above process limitations such inward radiation photons into the output light quantum extraction rate does not exceed 40%.
According to the above analysis can estimate the total LED electro-optical conversion efficiency of approximately 54%, which is the ideal case where the estimated result. Any omissions, any defects in the material in the manufacturing process will cause a decrease in the efficiency of energy conversion. Less than 5% of visible light conversion efficiency than incandescent, even compared with the current highest conversion efficiency of high-pressure sodium lamps, ceramic metal halide (electro-optical conversion efficiency of about 30%) is also very high, this is the LED very luring. person prospects reason.
As is known, the 1W energy is completely converted to 555nm wavelength of the yellow light produced when the light flux up to 683lm / W (683lm / W optical power equivalents) approximately 360lm / W, if all is converted to white. As estimated earlier in this article, in the ideal case 555nm yellow LEDs may reach up to about the highest luminous efficiency of 300lm / W, the above estimates are also far from being achieved. Reported the highest light efficiency LED actually only half of the ideal value, and in fact less than 1/4, this is what people On the LED there is great potential to be tapped on the high hopes reason.
The key is to improve the LED luminous efficiency to improve quantum extraction rate, which is to minimize the internal absorption of photons, this is slimline LED reasons. Highest luminous efficiency of ultra-thin (thickness of tens of nanometers) GaN LEDs under conductive film with a high reflective mirror membrane and the inner surface of the output window is made of rough structure, in order to reduce the photon inward reflection, however even so reported the highest light efficiency, but 150lm / W.
The above analysis is monochromatic LED is the monochromatic transformed into the white must then go through a quantum conversion, mostly by emission center wavelength of about 470nm blue LED excitation radiation spectrum center wavelength to 560nm broadband yellow phosphor, which made the blue-yellow mixed white LED, but this led lights efficiency will further reduce required. Photon efficiency can be estimated as follows:
If retained approximately 20% of the Blu-ray LED radiation output, with the remaining 80% of the Blu-ray excited yellow phosphor, in the best case, about 20% of the 80% of the Blu-ray photon absorption for phosphor, and the rest 80% transfer to the center wavelength of 560nm for broadband yellow radiation, this process resulted in an average of 16.1% of the quantum energy loss. Combine the previous data can be estimated that the total energy efficiency does not exceed 40%, and converted to white when the total light efficiency white LED white LED but up 150lm / W. If there is no other breakthroughs, this current white LED may be the highest light efficiency, this luminous efficiency HID lamps, high pressure sodium lamp or ceramic metal halide light sources, such as the current highest light efficiency is also high compared to some. Luminous efficiency has not yet actually achieved, and this half.
We have this experimental study, we use a company's production 1W high brightness blue LED, the center of the spectral radiation wavelength of 470nm see Fig.3 go except SMD LED Package were coated with different thickness of the center wavelength of the radiation is 560nm yellow phosphor coating, after treatment, to measure the emission spectrum thereof. Four typical case is selected from the 24 kinds of samples of different thickness, and its results are shown in Fig.4 a, b, c, d and Schedule. Lumen output in the best case (Fig.4 c) of 38lm (initial cold 50lm), color rendering index of 78.
A well-known multinational companies and technical personnel initial introduced their 1W white LED luminous efficiency reached 70lm / W, the normal operation of the pn junction temperature rise, 50lm / W luminous efficiency reduced.
The results obtained by the Japanese Institute of Materials Science, 2007 nano ceramic center is the highest, they used a center wavelength of 450nm InGaN blue LED and the photon conversion efficiency is high, and has a strong absorption peak at 450nm blue range, low temperature coefficient of the three kinds of phosphors test, the three phosphor were: α-sialon: Yb2 + α-sialon: Eu2 + and Sr2Si5, N8: Eu2 +. The characteristics of these phosphors is the luminous efficiency of the thermal decay is small, 85% of the initial value is still maintained at 150 ℃.
Made InGaN blue LED and phosphor white LED emission spectrum is shown as Fig.6, its luminous efficiency of 55lm / W, color temperature 4500K. This is the highest white LED luminous efficiency reports (I know, according to most of the testing domestic 1W white LED luminous flux 40lm below). No. 2 and No. 3, White LED emission spectrum is shown, such as mixed phosphor preproduction Fig.7, its color rendering index to 82, a color temperature of 4200K, the light efficiency is indeed reduced to 20lm / W.
As described above, the light emitting of the LED is on the load of the carriers (electrons) in the n-type semiconductor in the foreign potential role to overcome the electric potential of the barrier layer into the p-type semiconductor, and to generate a composite light-emitting hole-trapping. Usually the temperature coefficient of the semiconductor, its resistivity decreases as the temperature rises, the barrier potential will also drop to the bottom, at the same time the center wavelength of the radiation will be the longwave direction of drift the leaving luminous efficiency of the phosphor of the (redshift) decreased.
A large number of our businesses, investors, researchers and technical staff have to intervene in this situation, and the large-scale investment to develop LED R & D and production so far is estimated to have invested a total of RMB billions of dollars, in less than a decade achieved outstanding results, and the formation of large-scale industrial chain.
World especially LED white LED so emphasis on their underlying causes, this huge amount of energy consumption and the resulting energy shortages, rising prices, especially caused by the environment has become a very urgent task to make energy savings. A large part of the national energy consumption for lighting. In China and developed countries, electricity for lighting accounts for about total power generation capacity of 12 to 13%, which is a very substantial loss of energy. The light source is still used worldwide inefficient incandescent light source mainly from tapping the potential is very promising.
LED focuses many talents, brilliant achievements, some of the research department announced that they have developed LED reached 120lm / W or even 150 lm / W luminous efficiency under certain conditions. Thus most enterprises have also claimed the luminous efficiency of their product has reached 70lm / W, 90lm / W or higher, the light utilization than the radiation output of each LED optical radiation is directed, even ordinary light source alone directional reflection of the lamps lighting efficiency is higher, and therefore finds that LED is the best functional lighting source, and vigorously promoted to various areas of lighting, a few years ago has been declared the LED will largely replaced by compact fluorescent lamps in 2010, a large scale into the family lighting, and asserted that white LED is the best road illumination light source.
There is no doubt that after 20 years of development, the LED in the display area has been made entirely successful, without than with the theory and has become irreplaceable display devices. Fully display its features decorative lighting, made half of LED outstanding performance in the 2008 Olympic Games opening ceremony to shake the world. But must address the fact that greater limitations in terms of functional lighting white LED persists. China is already the world's largest LED production base and consumer market, LED application fields, but due to the restrictions of the current level of technology and performance, such devices are used for functional lighting is not to use their skills. So-called high power LED, currently on the market can find the most high-power devices, but 3W, even 10W devices in R & D to large-scale production, but for conventional lighting, especially the hundreds of watts of light sources used in road lighting single The granulocyte power err too small. White LED design a lighting project amount must be great, whether it is difficult to design or cost will be worth the wait.
Common evaluation Ⅱ LED light efficiency of LED high light efficiency and long life, and many manufacturers claim their products luminous efficiency of up to 90lm / W or higher, but these data are just some laboratory in the the test initial stage when the LED is still in the highest measured in the cold state data. The so-called 50,000 hours or 100,000 hours life just early estimate of the low-power color LED.
Its theoretical light efficiency can be estimated from the LED light-emitting mechanism. As known LED is the use of carrier recombination and light emission, all of its potential energy in the carrier recombination when transformed into light energy, its internal quantum efficiency of 100% of the purposes of this process alone. Carrier collision with the crystal lattice and the loss of energy in the medium when the composite contained the kinetic energy carried by the carrier, and the electricity is consumed to overcome the resistance of the external circuit are not converted into light. Taking into account the variety of additional energy, the actual carrier recombination within the quantum efficiency does not exceed 90%.
Photons generated when the carrier recombination, has a 50% chance for outgoing radiation, part of the 50% of the photons collide with the lattice and lattice absorption is converted into heat. Portion photon propagation in the different media at the interface will be reflected back to the original medium and is absorbed, addition, as the metal the omentum or transparent conductive film of the output window of the outer electrode also allow a portion of the photons reflected by absorption, these processes will reduce the LED quantum extraction rate, the extraction rate of 80% is located in this part of the photon quantum.
Of photons generated in the carrier recombination, a 50% chance of the incoming radiation, this part of the photons reach the underlying conductive film serves as a reflective mirror, a partially reflective converted to outward output optical photons in this section, however, the inwardly or outwardly The transmission during the collision with the crystal lattice and is partially absorbed, through different media interface will also be part of the reflected or refracted back to the original medium eventually be absorbed. Substrate mirror reflection efficiency and the above process limitations such inward radiation photons into the output light quantum extraction rate does not exceed 40%.
According to the above analysis can estimate the total LED electro-optical conversion efficiency of approximately 54%, which is the ideal case where the estimated result. Any omissions, any defects in the material in the manufacturing process will cause a decrease in the efficiency of energy conversion. Less than 5% of visible light conversion efficiency than incandescent, even compared with the current highest conversion efficiency of high-pressure sodium lamps, ceramic metal halide (electro-optical conversion efficiency of about 30%) is also very high, this is the LED very luring. person prospects reason.
As is known, the 1W energy is completely converted to 555nm wavelength of the yellow light produced when the light flux up to 683lm / W (683lm / W optical power equivalents) approximately 360lm / W, if all is converted to white. As estimated earlier in this article, in the ideal case 555nm yellow LEDs may reach up to about the highest luminous efficiency of 300lm / W, the above estimates are also far from being achieved. Reported the highest light efficiency LED actually only half of the ideal value, and in fact less than 1/4, this is what people On the LED there is great potential to be tapped on the high hopes reason.
The key is to improve the LED luminous efficiency to improve quantum extraction rate, which is to minimize the internal absorption of photons, this is slimline LED reasons. Highest luminous efficiency of ultra-thin (thickness of tens of nanometers) GaN LEDs under conductive film with a high reflective mirror membrane and the inner surface of the output window is made of rough structure, in order to reduce the photon inward reflection, however even so reported the highest light efficiency, but 150lm / W.
The above analysis is monochromatic LED is the monochromatic transformed into the white must then go through a quantum conversion, mostly by emission center wavelength of about 470nm blue LED excitation radiation spectrum center wavelength to 560nm broadband yellow phosphor, which made the blue-yellow mixed white LED, but this led lights efficiency will further reduce required. Photon efficiency can be estimated as follows:
If retained approximately 20% of the Blu-ray LED radiation output, with the remaining 80% of the Blu-ray excited yellow phosphor, in the best case, about 20% of the 80% of the Blu-ray photon absorption for phosphor, and the rest 80% transfer to the center wavelength of 560nm for broadband yellow radiation, this process resulted in an average of 16.1% of the quantum energy loss. Combine the previous data can be estimated that the total energy efficiency does not exceed 40%, and converted to white when the total light efficiency white LED white LED but up 150lm / W. If there is no other breakthroughs, this current white LED may be the highest light efficiency, this luminous efficiency HID lamps, high pressure sodium lamp or ceramic metal halide light sources, such as the current highest light efficiency is also high compared to some. Luminous efficiency has not yet actually achieved, and this half.
We have this experimental study, we use a company's production 1W high brightness blue LED, the center of the spectral radiation wavelength of 470nm see Fig.3 go except SMD LED Package were coated with different thickness of the center wavelength of the radiation is 560nm yellow phosphor coating, after treatment, to measure the emission spectrum thereof. Four typical case is selected from the 24 kinds of samples of different thickness, and its results are shown in Fig.4 a, b, c, d and Schedule. Lumen output in the best case (Fig.4 c) of 38lm (initial cold 50lm), color rendering index of 78.
A well-known multinational companies and technical personnel initial introduced their 1W white LED luminous efficiency reached 70lm / W, the normal operation of the pn junction temperature rise, 50lm / W luminous efficiency reduced.
The results obtained by the Japanese Institute of Materials Science, 2007 nano ceramic center is the highest, they used a center wavelength of 450nm InGaN blue LED and the photon conversion efficiency is high, and has a strong absorption peak at 450nm blue range, low temperature coefficient of the three kinds of phosphors test, the three phosphor were: α-sialon: Yb2 + α-sialon: Eu2 + and Sr2Si5, N8: Eu2 +. The characteristics of these phosphors is the luminous efficiency of the thermal decay is small, 85% of the initial value is still maintained at 150 ℃.
Made InGaN blue LED and phosphor white LED emission spectrum is shown as Fig.6, its luminous efficiency of 55lm / W, color temperature 4500K. This is the highest white LED luminous efficiency reports (I know, according to most of the testing domestic 1W white LED luminous flux 40lm below). No. 2 and No. 3, White LED emission spectrum is shown, such as mixed phosphor preproduction Fig.7, its color rendering index to 82, a color temperature of 4200K, the light efficiency is indeed reduced to 20lm / W.
As described above, the light emitting of the LED is on the load of the carriers (electrons) in the n-type semiconductor in the foreign potential role to overcome the electric potential of the barrier layer into the p-type semiconductor, and to generate a composite light-emitting hole-trapping. Usually the temperature coefficient of the semiconductor, its resistivity decreases as the temperature rises, the barrier potential will also drop to the bottom, at the same time the center wavelength of the radiation will be the longwave direction of drift the leaving luminous efficiency of the phosphor of the (redshift) decreased.
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