Yang Chunyu, School of Architecture and Urban Planning, Chongqing University
Abstract: Urban Landscape Lighting widespread use of LED, but some of negatively influence due to various reasons, people some incorrect understanding on the Night use, adverse effects article on LED physical basis and working principle, design method improper, LED Product quality issues, LED problems in the construction and management of night scenes were discussed, and the method of correctly using LEDs in urban night lighting was suggested.
Keywords : LED; night lighting; existing problems; method suggestion
LED lighting has developed rapidly in China and has been applied more and more widely in urban lighting fields, such as traffic signals, emergency lighting, advertising signs, commercial pedestrian streets, buildings (structures), urban squares, garden landscapes, etc. expand. LED as a kind of electric light source made by semiconductor technology is called the 21st century new generation light source. Because of its advantages of energy saving, long life and environmental protection, it is widely predicted that it will replace the traditional light source. Through the support of a series of scientific and technological projects such as 863 and tackling, China has initially formed a certain degree of LED industry chain. Reform and opening up have enabled China's economy to develop at a rapid pace. China has become one of the world's largest sources of light source and lighting. With the country's high attention to LED development and the rapid development of China's LED industry, China is expected to become one of the world's largest LED production bases and one of the largest countries in LED lighting applications. At present, LED has begun to spread in the field of urban night lighting in China. LEDs are widely used in night lighting in almost all major cities in the country. In particular, relevant departments in China have clearly proposed that the 2008 Beijing Olympic Games and the 2010 Shanghai World Expo will be used as an opportunity to promote semiconductors. The application of urban landscape lighting will further promote the wider use of LED in the urban lighting field in China. However, we should see that quite a few cities do not understand the characteristics of LEDs in night lighting, and there are many misunderstandings in the design, construction and maintenance management of night lighting, resulting in poor LED lighting effect in urban night lighting, and the evaluation is not high. In particular, there have been some abuses of LEDs, which have caused the city's night scenes to feel damaged and negatively affected. This has led some people to doubt the use of LEDs in urban night lighting, which has affected the reputation of LEDs in urban night lighting. If not resolved in time, Will definitely affect the healthy development of China's LED industry chain.
1. The main problems of current LED in urban night lighting application
1.1 Urban night lighting users do not understand the physical basis and working principle of LED
LED is a solid component that directly converts electrical energy into light energy. It is also called a light-emitting diode. Its basic structure is the basic unit PN junction of a semiconductor. The PN junction is a N-layer carrying electrons and a P-layer carrying a hole. The transition layer between. When a forward voltage is applied to the PN junction, a current flows from the P layer (hole layer) to the N layer (electron layer), and electrons are injected from the electron layer to the hole layer, and electrons and holes recombine to generate light. According to the law of conservation of energy, each time a photon is combined, its energy is hv=Eg, and the energy range of visible photons is Eg=1.9 ev (red) to Eg=3.0 ev (purple). In general, the internal quantum efficiency of LED materials is 10% to 15%, and the loss comes from material defects such as crystal defects and misalignment. The photon radiation in the LED wafer is only the first step in the manufacture of the LED. The light emitted by the PN junction is directed in all directions. When the photon is directed onto the upper surface of the wafer, most of the photons are reflected back from the inside of the interface to the wafer, only 1.5% to 2.0%. Left and right photons may escape the upper surface. A wafer has a total of 5 outer surfaces (top and four sides), so the total amount of photons that escape is 7.5% to 10%, and the remaining 90% of the photons are absorbed in the wafer, which is the case of the wafer in the air. When the wafer is embedded in an epoxy resin having a refractive index of 1.5, the photon escape rate is increased to about 20% to 25%. The reason for the low luminous efficiency is the internal photon absorption. Most of the photons cannot escape from the surface of the wafer and are refracted back. They are eventually absorbed inside. The more efficient wafer design is an inverted top-cut gold tower wafer. The LEDs made in the epoxy resin with the surfaces in a non-perpendicular state have an external quantum efficiency of 55% and can be higher. Luminous efficiency is an important indicator of which light source is used. Incandescent lamps and tungsten halogen lamps have luminous efficiencies of 12 to 24 lm/W and an average of 15 lm/W. High-efficiency fluorescent lamps and HID lamps have luminous efficiencies of 50 to 120 lm/W and an average of about 75 lm/W. A disadvantage of these sources is that only a small fraction of the electrical energy is converted into visible light. In theory, LEDs can achieve a conversion efficiency of 100% [1]. After decades of research, LED efficiency has improved rapidly. In semiconductor materials, different LEDs can be used to make different LEDs, and the different wavelengths of the luminescence will cause different perceptions of the human eye. According to the human eye's color-correcting habits, LEDs can be divided into: purple light (wavelength 400-430 nm), blue light (wavelength 430-470 nm), blue-green light (wavelength 470-500 nm), green light (wavelength is 500 ~ 530 nm), yellow-green light (wavelength 530 ~ 560 nm), yellow light (wavelength 560 ~ 590 nm), orange light (wavelength 590 ~ 620 nm), red light (wavelength 620 ~ 780 nm) [2 ]. Due to the narrow spectrum, concentrated energy, high luminous efficiency, pure color and color, the colored LED is widely used in urban landscape lighting.
1.2 Using the owner and government night lighting construction, management departments have misunderstandings in understanding
LEDs are widely advertised for their high efficiency and long life, which leads to some misunderstandings that LEDs can solve all the problems in night lighting. According to relevant information, to this end, the low-power LED device itself has a luminous efficiency of about 80 to 100 lm/W. The high-power high-brightness LED device itself has a luminous efficiency of about 50 to 70 lm/W. (50 lm/W means that only about 12% of the electricity is converted into light, which is expected to reach 150 lm/W in 2012 and 200 lm/W in 2020). The LED single lamp has low power and low luminous efficiency, and the power loss of the driving circuit accounts for more than 20% of the total power of the LED device. (Other ballast power consumption of the gas discharge lamp accounts for about 10% of the lamp power) [3] The volume of a single LED light source is too small, and the luminous flux output is too small. For night lighting, it often requires hundreds or even tens of thousands of LED light source combinations to replace the common lighting source, which brings LED combined light source and LED light fixture. And other issues. Due to the small emission angle of the LED light source and the strong directivity of the light source, the LED is not suitable for night illumination in any occasion. In terms of service life, the theoretical life of the LED device itself can reach 100,000 h [4], but the factors affecting the life of the LED in practical applications are too many and complicated, except for the materials, manufacturing processes and technologies of the LED device itself. The combination of particles, lamp design, control drive circuit performance, supporting components, heat dissipation, waterproof and dustproof, UV protection and high and low temperature changes, etc., affect the life of LED as a night lighting. The use of theoretical life as the propaganda of engineering application life can only damage the development of LED. Especially when some owners and government nightscape construction management departments were misunderstood by the misleading expectations of LEDs, and some problems appeared in engineering applications, the distrust of LEDs affected the application of LEDs in night lighting.
1.3 The improper design method of urban night lighting affects the use of LED
The use of LEDs in urban night lighting is relatively common (especially in some big cities). Because some night scene designers do not really understand the performance of LEDs, in the night lighting design, LEDs are not used in large quantities according to the objects to be illuminated, the characteristics of the attached carriers, functions and specific environments, and some cities rely on LEDs for night illumination and night scenes. The shaping method is single, the night scene is monotonous, and it does not reach the beauty that the city night scene should have; some use the matrix full method on the glass curtain wall of the government administrative office building, change various patterns, chasing the flashing form dynamic and gorgeous colors, Misunderstood that it is a nightclub; some in the hospital building and the environment, office buildings, residential buildings and residential areas with LED line, point light chasing light flashing, colorful and varied; some in the important building gable, top with LED plus some The shape of the components is composed of patterns, which destroy the architectural style during the day and change the architectural form at night; there are also some LEDs with light color changes everywhere in the school district and the quiet overflow area, which are strangely scattered, causing serious color light pollution; some are in a low background brightness environment. The use of many high-brightness LEDs causes glare that contrasts too much contrast; some use colored light near traffic lights Of the LED, resulting in the illusion of the driver and pedestrian traffic signals and so on. These incorrect designs have produced a false positive judgment for the general public, which has caused some cities to lose confidence in the use of LEDs in the night scene, which has affected the development of LEDs in the field of urban night lighting.
1.4 The quality of LED products for urban night lighting is mixed.
Due to the role of propaganda, people are full of good wishes for using LEDs in urban lighting. Some cities use it on a large scale, but after using it for a while, it is found that LEDs are not as long as the promotion mentioned. Some buildings cost millions of dollars to use LEDs for night lighting, but the installation is not normal after installation. Some LED lights are broken or the control system has problems, many improvements, multiple acceptances; some buildings, guardrails After a few months of using the LED, it broke a lot. The outline is not broken or the color change is abnormal. It has been criticized by the superiors and the masses. It has to be dismantled and replaced with other light source lamps. The loss is huge and has a great negative impact. LEDs are installed along the elevated light rails, causing fires, forcing light rail trains to stop, and so on. During the inspection, it was found that there are quite a few LEDs for night lighting that have serious quality problems. Among them, there are mainly quality problems such as the material and production process of the LED itself; there are a series of problems such as waterproofing and heat dissipation after a single LED is composed of several to hundreds of lamps. There are problems with the performance and quality of the driver circuit; there are control system problems and so on. These problems have affected the use effect and quality of LEDs in night lighting, and have had an adverse effect on the application of LEDs in night lighting.
1.5 Night lighting uses LED in construction, supervision and maintenance management problems
It is a very good thing to use LED as a new light source in night lighting. But LED has its own characteristics, because a considerable number of urban nightscape construction managers do not understand this problem, coupled with the improper propaganda of some manufacturers and media, people once thought that LED can solve all problems of night lighting. For example, night lighting energy consumption is a big problem; night scenes are mostly outdoor, there are various extreme climate problems; there is a problem of replacing high-rise super high-rise buildings with night lighting; there is a relationship between rain and dust, and the relationship between the life of the city; , flashing changes and other issues. LED energy saving, long life, rich and varied light colors, it seems that LED is in line with all the problems of solving these night lighting. Therefore, for some time, in some cities, in the construction of night scenes, as long as the LED night lighting scheme is used, the management department will think that the excellent scheme with high technology content will be passed. In the process of implementing the night scene, from the purchase of LED products to construction, and in the operation after the completion of the project, there is a lack of effective management system for LED quality review, engineering supervision and operation and maintenance, because everyone believes that LED has comprehensive advantages. When there is a problem in any of these links, the night scene project using LEDs cannot be turned on normally, or when there is a disagreement with the original design renderings and the beautiful scenes described by the night scene designer, people are not looking for the reasons from the above aspects ( Generally it is impossible to find it. The blame is the LED itself, and the LED is not good. This has caused a great blow to the use of LEDs in night lighting, and people have begun to doubt the role of LEDs in night lighting. This has a negative impact on the development of China's LED industry.
2. Suggestions for the correct use of LEDs in urban night lighting
LEDs are developing very fast in China, especially in night lighting. LED buried lights, underwater lights, emergency lights, garden lights, various sign lights, LED partial spot lights, LED line light sources, LED point light sources, etc., have greatly increased the color of the city night scene project effect. In particular, LEDs are good in color, relatively low in energy consumption, relatively long in life, low in voltage, safe in use, non-polluting, good in shock and shock resistance, small in size and easy to conceal, suitable for night lighting principles such as seeing no lights, etc. These are night scenes. Lighting use provides options. However, night lighting must be selected according to the characteristics of the LED itself. In design, some building gables, tops, etc. need a large area to cast light or show its structural shape, generally do not use LED, currently LED has no advantage of floodlighting. Do not use LEDs wherever wide beam angle illumination is required, because the LED source beam has a small emission angle, the source is too directional, and there is almost no light in a certain angle. The LED is suitable for a matrix in a contour, point source or glass curtain wall. Synthetic patterns, commercial places, places or carriers that require dynamic changes in color and the like. If the night view of the building is suitable for other light sources and LEDs to use together, it can bring out the advantages of LED. For example, some buildings require floodlighting, but generally the lamp body is too large to affect the building's daytime landscape. At this time, the LED floodlight can be selected, which is small in size and easy to conceal. This is an advantage that other light source floodlights do not have.
These need to pay more attention to nightscape design and building management. For example, when reviewing the design of the night scene, the design review should be strictly controlled, and the night scene scheme that can not fully utilize the LED's strengths during design is not used. In the implementation, the quality of the LEDs for the purchase of night scenes is strictly controlled. We do not advocate the purchase of only low-priced products. All kinds of supporting facilities and accessories such as LED lamps that do not meet the quality requirements are forbidden to purchase, and the LED products are strictly closed. Strict engineering supervision system shall be implemented during the construction process. Any failure to meet the construction and installation specifications and requirements must be corrected to prevent irregular construction and installation. After the completion of construction, the inspection and acceptance system shall be strictly implemented and acceptance shall be carried out in accordance with the normative standards. In the LED night scene project put into use, it is necessary to establish an operation and maintenance system, equipped with corresponding maintenance personnel, and make inspection records for operation and maintenance and peacetime. Once problems are found, timely maintenance and discharge should be carried out to enable the LED night lighting project to operate normally. LED night scene project always maintains a normal operating state, maintaining the reputation of LED in night lighting.
3. Conclusion
LED as a new light source with a bright future, although white LEDs have a long way to go to replace other light sources with functional lighting, but it has shown its strong advantages in urban landscape lighting. LED has the advantages of energy saving, safety, environmental protection, rich color, long life, small size, short response time, etc. It is very suitable for urban night lighting. As long as we use LEDs to enhance the correct guidance for urban night lighting, adopt the correct design methods and strengths and avoid weaknesses, as LED performance continues to improve, prices fall, and LED application research is further deepened, there is reason to believe that urban night lighting applications Another climax of LED is coming. Our professional and technical personnel should do some specific and effective work for the arrival of this climax, which is worthy of our joint research.
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About the Author:
Yang Chunyu, male, professor and Ph.D., School of Architecture and Urban Planning, Chongqing University, major research interests: urban light environment and urban lighting. He has published more than 60 papers on lighting, and won two provincial and second prizes, one patent. Hosted to participate in the National Natural Science Foundation of China (lighting), the National Doctoral Fund (lighting), participated in the two national lighting standards, specifications and two local lighting standards in Chongqing, presided over lighting project planning and design There are dozens of items.
He holds academic positions: member of the Organizing Committee of the International Commission on Illumination (CIE), deputy secretary-general of the China Lighting Society, deputy director of the Outdoor Lighting Committee of the China Lighting Society, reviewer of China Zhongzhao Lighting Award, and expert of the Green Lighting Demonstration Engineering Group of the Ministry of Construction. Editor of the China Lighting Yearbook, chairman of the Chongqing Lighting Society, editor of "Lights and Lighting" magazine.
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