Recently, Liu Muqing, professor of Fudan University, director of the Institute of Electric Light Sources, and director of the Department of Light Source and Lighting Engineering, analyzed the application of LED in tunnel lighting and caused a heated discussion in the industry. The main light sources for tunnel lighting are fluorescent lamps, high-pressure sodium lamps and metal halide lamps. The characteristics of LEDs determine its future potential in tunnel lighting.
First, the main light source comparison of tunnel lighting
At present, the light source of tunnel illumination mainly includes high-pressure sodium lamp, fluorescent lamp, metal halide lamp, etc. Among them, high-pressure sodium has high light efficiency, less ultraviolet radiation, can be ignited at any position, is shock-resistant, and has a long service life, in tunnel lighting, especially in cities such as mountains. A large number of tunnels are used, and fluorescent lamps, metal halide lamps, and the like have been widely used in urban tunnel lighting in recent years. LED is a light source that has developed rapidly in recent years. Its performance indicators such as light efficiency are rapidly increasing and the price is rapidly decreasing. Therefore, it has been gradually applied in directional lighting such as road lighting while being successfully applied in display and landscape lighting.
Second, the characteristics of LED as a tunnel illumination source
1, the overall light effect of the LED tunnel light
In addition to the light efficiency of the LEDs used, the overall efficiency of the LED tunnel light is also related to three factors: the light utilization achieved by the secondary optical design, the good heat dissipation to ensure the LED output luminous flux maintenance performance and the efficiency of the LED drive circuit. . The efficiency of the above several parts is multiplied to obtain the overall luminous efficacy of the LED tunnel light.
Through the study of the LED light-emitting mechanism, it can be inferred that the radiation spectrum efficiency of the LED can reach 350 lm/w. Since the LED light-emitting mechanism is a cold light source, and the spectrum of the radiation is all in the visible light range, the actual efficiency is expected to be closer to the theoretical value. Even considering the limitations of the process, the actual LED efficacy is half the theoretical value. The improvement of light efficiency means the improvement of energy utilization efficiency. When the production process of LED is mature, the energy-saving advantages of LED will be highlighted in comparison with traditional tunnel illumination sources.
Secondly, compared with traditional light sources, LEDs are small in size and can even be treated as point sources in many applications, which gives the luminaires a great deal of flexibility in their optical design. At the same time, in the conventional light source luminaire, the light source occlusion and absorption due to the large size of the light source does not exist in the LED luminaire.
Once again, the LED only emits light into the half space, which means that without any form of reflector, the light from the light source can also be directed to the illuminated surface. This feature determines that the LED lamp is expected to achieve more than 90% efficiency of the lamp. . At the same time, a high optical utilization rate is achieved through a reasonable optical design.
The above is the possible advantages of LED for tunnel lighting in terms of overall light efficiency, but how to turn its advantages into practical application products still needs to solve many technical problems. The LED is a light source that is very different from a conventional light source such as a high-pressure sodium lamp. For tunnel illumination, it is not possible to simply replace the existing light source with an LED, and it is not possible to simply illuminate the LED for tunnel illumination. How to integrate the various components of the LED tunnel luminaire to achieve the maximum utilization of the luminous flux of the light source and maximize the energy saving of the lighting is a challenge we face.
2, LED tunnel lighting life
Due to the 24-hour lighting, the tunnel lighting is 8760 hours a year, and the continuous lighting is about 35,000 hours in 4 years. And because the replacement of the lamps in the tunnel is very troublesome, the life expectancy of the tunnel lamps is very high.
The main influences on the life of the luminaire are the light source and the ballast, and the life of the lamp and the glass is very long. In conventional light sources, including fluorescent lamps, metal halide lamps, and high-pressure sodium lamps, the life of the lamps is shorter than that of the ballasts, and thus the method of replacing the lamps often extends the overall life of the lamps. In LED luminaires, the theoretical life of LED devices is very long, so the life of LED drivers becomes a bottleneck.
In the traditional light source, the electrodeless fluorescent lamp is a variant of the fluorescent lamp, and its life is very long. It is generally considered to be more than 50,000 hours, but its lighting is a high-frequency AC signal, and the corresponding ballast technology is more complicated, so its life will be the main bottleneck.
3. Market application of LED tunnel lights
From the development of the LED market and the continuous improvement of production technology, the current problem of restricting the price of LED as an illumination source will be gradually solved. The application of LED in various lighting will be gradually popularized and deepened. According to industry analysis, the price decline of LEDs is down by half every 24 months. Therefore, with the rapid decline of LED prices, compared with traditional light sources, the advantages of LEDs make the lamps more efficient, easy to use, environmentally friendly, and long life, especially in directional lighting, including tunnel lighting. The field will be quickly promoted.
At present, LED applications are mostly used in mountain road tunnels. The application effects are different, and there are still many problems in the application, such as large light decay, high junction temperature, unreasonable structure of the lamp, poor illumination uniformity, long life of the driving power supply, and uneven quality. When designing LED lighting applications for the Yangtze River Tunnel, it is necessary to strengthen system research and form technical indicators and system design to ensure the feasibility of LED application in Shanghai Yangtze River Tunnel Project.
Third, the application of LED in Shanghai Yangtze River Tunnel Lighting Project
The Shanghai Yangtze River Tunnel Bridge (Chongming River Crossing) is a major national construction project in the 11th Five-Year Plan. After nearly two years of experimentation, the engineer decided to use LEDs for the main lighting in the tunnel of the project.
1. Introduction to the Shanghai Yangtze River Tunnel Bridge (Chongming River Crossing)
Shanghai Shanghai Yangtze River Tunnel Bridge (Chongming River Crossing) project is located in the south bank of Shanghai's northeastern Yangtze River and Beigang waters. It is a large-scale transportation infrastructure project in the Yangtze River estuary in China and an important part of the road from Shanghai to Xi'an. The construction of the project will form and improve the large-scale coastal transportation channel, give full play to the geographical advantages of Shanghai, promote the economic development of the coastal development zone to a new level, further realize the national "two-way strategy", and enhance and strengthen the radiation function of Shanghai. It is very necessary and has very important strategic significance. The project started from the No. 5 Ditch in Pudong New Area of ​​Shanghai, and arrived at Chenjia Town of Chongming County via Changxing Island. The total length is 25.5KM. It adopts the North Tunnel North Bridge plan and is designed according to the two-way six-lane expressway standard, including the Yangtze River in the port of Vietnam. The tunnel project has a total length of 8.95KM. The Jiangzhong round tunnel is constructed by shield method, with a length of 7.5KM and a design speed of 80KM/S. The tunnel is intended to use LED lighting technology in the basic section to achieve environmental protection and energy conservation in the tunnel operation process. This plan is a step forward and requires a large amount of research, testing and evaluation work, and it has a strong research and exploration nature. The Yangtze River Tunnel Command, the Institute of Electric Light Sources of Fudan University; the Shanghai Yangtze River Tunnel Engineering Semiconductor Lighting Application Group established by the Shanghai Tunnel Design and Research Institute has done a lot of work in the field of technical specification development and testing, and accumulated a large number of First-hand data, and explored a set of LED tunnel lighting evaluation methods, for the similar projects to provide a reference for the promotion of LED as a lighting source has created a powerful push.
2. Application research of LED in Shanghai factory tunnel engineering
LED applications and tunnel lighting are still in their infancy, and problems such as light source reliability, lamp safety, and reasonable structure of lamps have not been finalized, and there is no relevant experience to follow. Therefore, research focuses on this, starting from the aspects of optics, electricity and lighting effects, and finally forming LED lighting solutions and LED lighting technical requirements to facilitate engineering applications.
LED is in a rapid development stage, and it has certain unpredictability. There is a corresponding public relations difficulty in the alternative research of engineering lighting system. Through a large number of data collection and research comparisons, it is proved that the use of LED luminaires in re-tunnel lighting can achieve energy-saving purposes, and the new LED structure form has no large bottleneck in reliability realization compared with luminaires using traditional light sources. The energy-saving characteristics of LED lamps are mainly reflected in the following two points: First, the well-structured LED tunnel lights combined with the scientific overall lighting scheme can achieve higher light utilization than high-pressure sodium lamps and long tubular fluorescent lamps, that is, high effective luminous efficiency, This achieves energy saving in lighting; secondly, convenient stepless dimming is one of the biggest advantages and highlights of LED as a new light source, combined with intelligent lighting control system, reducing the power of the lighting system during periods of low operating load, this mode of operation At the same time, the lighting effect inside the tunnel is guaranteed and energy conservation is realized. The luminous efficiency of high-power white LEDs varies greatly depending on the technical level and production conditions of different manufacturers. At present, most domestic manufacturers produce/package chips, and their light efficiency indicators are not high. Their LED products cannot achieve lighting energy saving compared with traditional light sources. Therefore, in the application research of this project, the mature power products of the world-class well-known brands are required to be used on the LED chips, and the low thermal resistance is selected on the package to ensure the stability, reliability and high efficiency of the power LED operation.
LED as a new light source, there are still many problems to be solved for tunnel lighting. To evaluate the overall quality of LED luminaires, it is necessary to study the optical, electrical and lighting effects of LEDs for tunnel illumination according to the overall scheme of tunnel lighting to determine the optimal LED tunnel lighting requirements for light distribution, control, reliability, etc. And accordingly, the corresponding detection methods and means are established. At present, the efficacy of the power type white LED is equivalent to that of the fluorescent lamp. Whether it achieves the energy saving goal, it is also necessary to evaluate the efficiency of the lamp between the two. The LED has the advantage of combining the secondary optical design of the lamp. As long as the lighting design and the post-manufacturing level are grasped, the energy saving index superior to the fluorescent lamp can be achieved.
Currently, a big bottleneck in limiting power LED applications is heat dissipation. Since LEDs are semiconductor devices, an increase in junction temperature can result in variations and attenuations in all aspects of the device. Specific to LED, this change is mainly reflected in three aspects: reducing the light output of the LED, shortening the life of the device, causing the main wavelength of the LED to emit light, which causes the color of the light source to shift. These are all very important indicators in our lighting applications. Therefore, how to set the thermal parameters in the amount to ensure the corresponding LEDs work properly, this work is very important. Many of the LED lighting products on the market now give temperature rise indicators based on the difference between the temperature of the lamp housing and the ambient temperature. There are certain limitations in using this method to measure the heat dissipation performance of the lamp. Because the performance related to the performance of the LED is directly related to the junction temperature of the device PN junction, the final indicator of current concern is the junction temperature, and the selection of different lamps, the material of the lamp, the production process and the design of the heat dissipation are very good. The big difference is that the thermal resistance from the device PN junction to the lamp housing is very different. Under such conditions, it is unscientific to judge the heat dissipation performance of the lamp by the temperature rise of the lamp housing temperature relative to the ambient temperature. The most accurate method is to directly measure the temperature of the PN junction of the device selected by the luminaire, and measure the thermal design of the luminaire by the difference between the junction temperature and the ambient temperature.
Fourth, the conclusion
In the big issue of exploring how LEDs enter the field of lighting, tunneling with LEDs is also a new field. From the theoretical analysis, there is no big technical bottleneck for LED to enter tunnel lighting. It can be seen from the limited related engineering cases that the results and effects brought by this technology are obvious and gratifying. In order to ensure the steady advancement of key projects, and to explore the process of LED entering the lighting field, combined with the Yangtze River Cross-river Tunnel Project, the project team has done a lot of related work. At present, LED is used as the main lighting in tunnel lighting. It is believed that a series of research data and field test parameters will become valuable first-hand information for the project and LED promotion. I believe that LED lighting will become a tunnel in the future. The backbone of lighting applications!
First, the main light source comparison of tunnel lighting
At present, the light source of tunnel illumination mainly includes high-pressure sodium lamp, fluorescent lamp, metal halide lamp, etc. Among them, high-pressure sodium has high light efficiency, less ultraviolet radiation, can be ignited at any position, is shock-resistant, and has a long service life, in tunnel lighting, especially in cities such as mountains. A large number of tunnels are used, and fluorescent lamps, metal halide lamps, and the like have been widely used in urban tunnel lighting in recent years. LED is a light source that has developed rapidly in recent years. Its performance indicators such as light efficiency are rapidly increasing and the price is rapidly decreasing. Therefore, it has been gradually applied in directional lighting such as road lighting while being successfully applied in display and landscape lighting.
Second, the characteristics of LED as a tunnel illumination source
1, the overall light effect of the LED tunnel light
In addition to the light efficiency of the LEDs used, the overall efficiency of the LED tunnel light is also related to three factors: the light utilization achieved by the secondary optical design, the good heat dissipation to ensure the LED output luminous flux maintenance performance and the efficiency of the LED drive circuit. . The efficiency of the above several parts is multiplied to obtain the overall luminous efficacy of the LED tunnel light.
Through the study of the LED light-emitting mechanism, it can be inferred that the radiation spectrum efficiency of the LED can reach 350 lm/w. Since the LED light-emitting mechanism is a cold light source, and the spectrum of the radiation is all in the visible light range, the actual efficiency is expected to be closer to the theoretical value. Even considering the limitations of the process, the actual LED efficacy is half the theoretical value. The improvement of light efficiency means the improvement of energy utilization efficiency. When the production process of LED is mature, the energy-saving advantages of LED will be highlighted in comparison with traditional tunnel illumination sources.
Secondly, compared with traditional light sources, LEDs are small in size and can even be treated as point sources in many applications, which gives the luminaires a great deal of flexibility in their optical design. At the same time, in the conventional light source luminaire, the light source occlusion and absorption due to the large size of the light source does not exist in the LED luminaire.
Once again, the LED only emits light into the half space, which means that without any form of reflector, the light from the light source can also be directed to the illuminated surface. This feature determines that the LED lamp is expected to achieve more than 90% efficiency of the lamp. . At the same time, a high optical utilization rate is achieved through a reasonable optical design.
The above is the possible advantages of LED for tunnel lighting in terms of overall light efficiency, but how to turn its advantages into practical application products still needs to solve many technical problems. The LED is a light source that is very different from a conventional light source such as a high-pressure sodium lamp. For tunnel illumination, it is not possible to simply replace the existing light source with an LED, and it is not possible to simply illuminate the LED for tunnel illumination. How to integrate the various components of the LED tunnel luminaire to achieve the maximum utilization of the luminous flux of the light source and maximize the energy saving of the lighting is a challenge we face.
2, LED tunnel lighting life
Due to the 24-hour lighting, the tunnel lighting is 8760 hours a year, and the continuous lighting is about 35,000 hours in 4 years. And because the replacement of the lamps in the tunnel is very troublesome, the life expectancy of the tunnel lamps is very high.
The main influences on the life of the luminaire are the light source and the ballast, and the life of the lamp and the glass is very long. In conventional light sources, including fluorescent lamps, metal halide lamps, and high-pressure sodium lamps, the life of the lamps is shorter than that of the ballasts, and thus the method of replacing the lamps often extends the overall life of the lamps. In LED luminaires, the theoretical life of LED devices is very long, so the life of LED drivers becomes a bottleneck.
In the traditional light source, the electrodeless fluorescent lamp is a variant of the fluorescent lamp, and its life is very long. It is generally considered to be more than 50,000 hours, but its lighting is a high-frequency AC signal, and the corresponding ballast technology is more complicated, so its life will be the main bottleneck.
3. Market application of LED tunnel lights
From the development of the LED market and the continuous improvement of production technology, the current problem of restricting the price of LED as an illumination source will be gradually solved. The application of LED in various lighting will be gradually popularized and deepened. According to industry analysis, the price decline of LEDs is down by half every 24 months. Therefore, with the rapid decline of LED prices, compared with traditional light sources, the advantages of LEDs make the lamps more efficient, easy to use, environmentally friendly, and long life, especially in directional lighting, including tunnel lighting. The field will be quickly promoted.
At present, LED applications are mostly used in mountain road tunnels. The application effects are different, and there are still many problems in the application, such as large light decay, high junction temperature, unreasonable structure of the lamp, poor illumination uniformity, long life of the driving power supply, and uneven quality. When designing LED lighting applications for the Yangtze River Tunnel, it is necessary to strengthen system research and form technical indicators and system design to ensure the feasibility of LED application in Shanghai Yangtze River Tunnel Project.
Third, the application of LED in Shanghai Yangtze River Tunnel Lighting Project
The Shanghai Yangtze River Tunnel Bridge (Chongming River Crossing) is a major national construction project in the 11th Five-Year Plan. After nearly two years of experimentation, the engineer decided to use LEDs for the main lighting in the tunnel of the project.
1. Introduction to the Shanghai Yangtze River Tunnel Bridge (Chongming River Crossing)
Shanghai Shanghai Yangtze River Tunnel Bridge (Chongming River Crossing) project is located in the south bank of Shanghai's northeastern Yangtze River and Beigang waters. It is a large-scale transportation infrastructure project in the Yangtze River estuary in China and an important part of the road from Shanghai to Xi'an. The construction of the project will form and improve the large-scale coastal transportation channel, give full play to the geographical advantages of Shanghai, promote the economic development of the coastal development zone to a new level, further realize the national "two-way strategy", and enhance and strengthen the radiation function of Shanghai. It is very necessary and has very important strategic significance. The project started from the No. 5 Ditch in Pudong New Area of ​​Shanghai, and arrived at Chenjia Town of Chongming County via Changxing Island. The total length is 25.5KM. It adopts the North Tunnel North Bridge plan and is designed according to the two-way six-lane expressway standard, including the Yangtze River in the port of Vietnam. The tunnel project has a total length of 8.95KM. The Jiangzhong round tunnel is constructed by shield method, with a length of 7.5KM and a design speed of 80KM/S. The tunnel is intended to use LED lighting technology in the basic section to achieve environmental protection and energy conservation in the tunnel operation process. This plan is a step forward and requires a large amount of research, testing and evaluation work, and it has a strong research and exploration nature. The Yangtze River Tunnel Command, the Institute of Electric Light Sources of Fudan University; the Shanghai Yangtze River Tunnel Engineering Semiconductor Lighting Application Group established by the Shanghai Tunnel Design and Research Institute has done a lot of work in the field of technical specification development and testing, and accumulated a large number of First-hand data, and explored a set of LED tunnel lighting evaluation methods, for the similar projects to provide a reference for the promotion of LED as a lighting source has created a powerful push.
2. Application research of LED in Shanghai factory tunnel engineering
LED applications and tunnel lighting are still in their infancy, and problems such as light source reliability, lamp safety, and reasonable structure of lamps have not been finalized, and there is no relevant experience to follow. Therefore, research focuses on this, starting from the aspects of optics, electricity and lighting effects, and finally forming LED lighting solutions and LED lighting technical requirements to facilitate engineering applications.
LED is in a rapid development stage, and it has certain unpredictability. There is a corresponding public relations difficulty in the alternative research of engineering lighting system. Through a large number of data collection and research comparisons, it is proved that the use of LED luminaires in re-tunnel lighting can achieve energy-saving purposes, and the new LED structure form has no large bottleneck in reliability realization compared with luminaires using traditional light sources. The energy-saving characteristics of LED lamps are mainly reflected in the following two points: First, the well-structured LED tunnel lights combined with the scientific overall lighting scheme can achieve higher light utilization than high-pressure sodium lamps and long tubular fluorescent lamps, that is, high effective luminous efficiency, This achieves energy saving in lighting; secondly, convenient stepless dimming is one of the biggest advantages and highlights of LED as a new light source, combined with intelligent lighting control system, reducing the power of the lighting system during periods of low operating load, this mode of operation At the same time, the lighting effect inside the tunnel is guaranteed and energy conservation is realized. The luminous efficiency of high-power white LEDs varies greatly depending on the technical level and production conditions of different manufacturers. At present, most domestic manufacturers produce/package chips, and their light efficiency indicators are not high. Their LED products cannot achieve lighting energy saving compared with traditional light sources. Therefore, in the application research of this project, the mature power products of the world-class well-known brands are required to be used on the LED chips, and the low thermal resistance is selected on the package to ensure the stability, reliability and high efficiency of the power LED operation.
LED as a new light source, there are still many problems to be solved for tunnel lighting. To evaluate the overall quality of LED luminaires, it is necessary to study the optical, electrical and lighting effects of LEDs for tunnel illumination according to the overall scheme of tunnel lighting to determine the optimal LED tunnel lighting requirements for light distribution, control, reliability, etc. And accordingly, the corresponding detection methods and means are established. At present, the efficacy of the power type white LED is equivalent to that of the fluorescent lamp. Whether it achieves the energy saving goal, it is also necessary to evaluate the efficiency of the lamp between the two. The LED has the advantage of combining the secondary optical design of the lamp. As long as the lighting design and the post-manufacturing level are grasped, the energy saving index superior to the fluorescent lamp can be achieved.
Currently, a big bottleneck in limiting power LED applications is heat dissipation. Since LEDs are semiconductor devices, an increase in junction temperature can result in variations and attenuations in all aspects of the device. Specific to LED, this change is mainly reflected in three aspects: reducing the light output of the LED, shortening the life of the device, causing the main wavelength of the LED to emit light, which causes the color of the light source to shift. These are all very important indicators in our lighting applications. Therefore, how to set the thermal parameters in the amount to ensure the corresponding LEDs work properly, this work is very important. Many of the LED lighting products on the market now give temperature rise indicators based on the difference between the temperature of the lamp housing and the ambient temperature. There are certain limitations in using this method to measure the heat dissipation performance of the lamp. Because the performance related to the performance of the LED is directly related to the junction temperature of the device PN junction, the final indicator of current concern is the junction temperature, and the selection of different lamps, the material of the lamp, the production process and the design of the heat dissipation are very good. The big difference is that the thermal resistance from the device PN junction to the lamp housing is very different. Under such conditions, it is unscientific to judge the heat dissipation performance of the lamp by the temperature rise of the lamp housing temperature relative to the ambient temperature. The most accurate method is to directly measure the temperature of the PN junction of the device selected by the luminaire, and measure the thermal design of the luminaire by the difference between the junction temperature and the ambient temperature.
Fourth, the conclusion
In the big issue of exploring how LEDs enter the field of lighting, tunneling with LEDs is also a new field. From the theoretical analysis, there is no big technical bottleneck for LED to enter tunnel lighting. It can be seen from the limited related engineering cases that the results and effects brought by this technology are obvious and gratifying. In order to ensure the steady advancement of key projects, and to explore the process of LED entering the lighting field, combined with the Yangtze River Cross-river Tunnel Project, the project team has done a lot of related work. At present, LED is used as the main lighting in tunnel lighting. It is believed that a series of research data and field test parameters will become valuable first-hand information for the project and LED promotion. I believe that LED lighting will become a tunnel in the future. The backbone of lighting applications!
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