The application of LEDs (light-emitting diodes) can be said to be everywhere. As a kind of semiconductor luminescent material, compared with other luminescent materials, LEDs are eclipsed by other green materials because of their advantages of green, high efficiency, reliability and durability. As the cost of high-power LEDs continues to decrease, it is possible to gradually replace traditional lamps. The application of LED light source in road lighting has become a hot spot in the semiconductor lighting industry in recent years. LED device products are applied to street lamps. What are the special requirements for technology? What are the advantages of LED street lamps compared with current street lamps? What are the shortcomings? How to solve it? Industry experts have explained from different aspects.
Formulating national standards is a powerful means of popularizing and popularizing
LED as a street lamp mainly has the following advantages or features: high luminous efficiency, low reflection loss of lamps, saving energy by 70%; with digital control brightness function, more power saving; no need for high voltage, high security; with software can remotely control remote brightness; Provide high-brightness and high-color illumination light source under special circumstances such as accidents, fog, rain, etc.; easy installation and maintenance; module installation, no unnecessary wiring; no light pollution or waste; long life means no need to often Replacement reduces the potential for traffic disruptions and reduces the maintenance costs paid for this. It has been calculated that the use of LED street lights is superior to high-pressure sodium lamps in terms of laying cost, power consumption cost and life in addition to the cost of single lamps and the cost of initial installations compared to high-pressure sodium lamps.
The main technical problems faced by LED street lamps are: output power and luminous flux, secondary optical design, thermal design and power system design. The improvement of output power and luminous flux also needs to be further improved from the basic level of high-power white LED epitaxial technology and chip technology. In terms of secondary optical design, the radiation forms of LEDs are Lambertian, side-fire, batwing and concentrating. In the field of road lighting, according to the design experience, Lambertian and batwing are more suitable. Through the secondary optical design, the illumination range and luminosity curve of LED meet the requirements of road lighting. Heat dissipation is one of the key problems that LED street lamps need to solve. Because LED street lamps have high brightness requirements and large heat generation, and outdoor use environment is harsh, if the heat dissipation is not good, it will directly lead to rapid aging of LEDs, and the stability will be reduced. The heat dissipation of the LED itself is good. Because the street lamp has the characteristics of outdoor nighttime use, the heat dissipation surface is located on the side to facilitate the natural convection heat dissipation of the air. The power system of LED street lamps is also different from traditional light sources. The combination of low energy consumption, low operating voltage and low output power and low output voltage of solar modules is very suitable. How to make a group of LEDs tightly compressed together safe, Reliable work is also an indicator of LED street lights.
Based on the above analysis of the market prospects and technical issues of LED street lamps, it can be seen that the factors affecting their application are:
First, the high cost of LED street lights is not conducive to popularization. Although the heat dissipation problem of LED street lamps has been initially solved, the excessive price and overweight lamp heads still hinder the popularity of LED street lamps.
Second, the reliability of the modularization of LED street lamps still needs to be strengthened, and LED street lamps may be ineffective due to driving circuits and the like.
Third, LED street lights, whether single-point or multi-point light sources, have the problem of heat dissipation. As for the street lamp with 250W high-pressure sodium lamp, due to the mature technology, the heat dissipation is very good. Even if it works for 5,000 hours, the light decay is still small, and the luminous efficiency can reach more than 70%. With the current technology, high-power LED street lamps under the same conditions are difficult to solve due to heat dissipation problems, and the light decay is large, and the luminous efficiency will drop to 30%. If you want to increase the light efficiency by increasing the voltage and current, it is easy to cause LED chips. The phenomenon of damage.
Fourth, LED street lights have a short range, so LED street lights need to further strengthen research on how to work at higher altitudes. In addition, the development of national LED road lighting standards is also a very powerful means to popularize LED street lights.
Heat dissipation and reliability are the main factors affecting the application
There are two ways to use LED light sources. One is to use traditional low-power LEDs as a combination, usually up to hundreds or even hundreds, and the power supply design is complicated. The other is to use a high-power tube as a light source, which is more expensive. Both methods inevitably require thermal design and operational reliability as the main design considerations. Most of them are used in government demonstration projects, and there are few projects in real market operation. There are many application examples in foreign countries, but The biggest drawbacks are still reliability, lumens and price. Many projects do not show the advantages of long life due to poor LED quality. In addition, from the perspective of cost and market, LED is used as an illumination source. Whether it is used in combination with solar energy, it is necessary to take different routes in design, and it is not completely developed as a light source.
LED device products are applied to street lamps. The special technical requirements are mainly to design LED light intensity and illumination angle. In addition, due to the combination of multiple LEDs, the illumination design should take into account the illumination area. Sex.
Advantages of LED street light and ordinary street light: energy saving, environmental protection, easy to adapt to low voltage, and can also be directly matched with solar energy system, without additional inverter and conversion process, can achieve maximum energy utilization.
Insufficient: the illumination angle is small and uneven, the color rendering index is low, and the optical and heat dissipation design is complicated.
Technical deficiencies: The luminous flux under the current technology is not enough, the light efficiency is too low, and the quality is difficult to guarantee.
Solution: The application of LED products to street lamps requires special design and special standards (using the test data of traditional light sources to evaluate LED light sources is often not objective).
The application of LED to street lamps has inherent advantages and disadvantages. The advantages are: First, LED as a point source, if the design is reasonable, it can directly solve the problem of secondary light extraction and optical loss that traditional spherical light source must rely on light emission to solve; second, uniformity of light irradiation surface The degree is controllable, theoretically it can be completely uniform in the target area, which can also avoid the waste of light in the traditional light source "light under the light" phenomenon; third, the color temperature is optional, so that in different applications, it is also improved An important way to reduce efficiency and reduce costs; fourth, there is still a lot of room for technological progress.
Disadvantages (factors affecting the promotion and application of street lamps): The current price is too high, the luminous flux is low, and the current LED illumination source with the same illumination design is about 4 times the price of the traditional light source (although in the street lamp products, the total cost of the light source is not high) Therefore, the cost increase ratio in the engineering installation will not be too high, and the application space is still relatively large), which is unbearable in civilian use. Current design and manufacturing standards are confusing, and the damage ratio is high, which affects the life expectancy of LEDs.
Recommendation: Unify the LED standard, improve the quality stability, establish a market competition coordination organization, avoid vicious competition, vigorously promote the quality concept of LED, avoid the influence of bad examples, let people accept the LED from the idea can actually achieve its long life. The advantages of improving the level of selection and use of LEDs.
The demand for high-power LEDs for white light will reach 300 million
LED devices are applied to street lamps. The technical requirements are mainly reflected in the following two aspects: First, good luminous efficiency stability, can not be attenuated too fast. Secondly, the consistency and maintainability of the light color is better, and it cannot be changed by using the white light color for a long time. Both of these points require the overall heat dissipation of the luminaire to be good, and the optical design must be in place.
The advantages of LED street lights compared with the current ordinary high-pressure sodium lamp street lights are as follows
First, energy saving: At present, the luminous efficiency of white LED is about 80lm/W, which can save 50%~60% compared with traditional high-pressure sodium lamps. With the rapid improvement of LED efficiency, semiconductor street lamps have shown great potential in energy saving.
Second, low maintenance cost: Based on the current technical level and test results, the high-power LED light source can be used normally for 10 years without replacement, and the traditional high-pressure sodium lamp should be replaced once every one and a half years. The use of semiconductor light source can greatly reduce maintenance costs. .
Third, good color rendering: LED's color rendering index is high (75~80), people's reaction speed is fast, the road surface looks brighter, feels more comfortable, and the driver feels safer. The high-pressure sodium lamp has a narrow spectrum and poor color rendering (20~40), and it feels dim.
The main shortcomings are as follows:
First, the luminous efficiency is not high enough: although the luminous efficiency of high-power white LEDs in the laboratory has exceeded 100lm/W, the luminous efficiency of mass-produced, cost-effective high-power white LEDs is still around 60lm/W, saving energy. The advantages have not been fully realized.
Second, the ground has a low reflectivity to the LED light: due to the spectral characteristics of the current white LED, the road surface and surrounding objects have low reflectivity, so the brightness of the road surface is low, which is a weak point compared with the yellow light of the sodium lamp.
The current luminous efficiency of high-power white LED light source is still in the stage of about 70lm/W~80lm/W. The theoretical luminous efficiency can reach about 300lm/W, so there is still a very large development space in technology. At the same time, semiconductor light source street lamps are currently in the initial stage of industrial development. There is still much room for improvement in terms of improving heat dissipation efficiency, drive control system optimization, and light distribution design, and a large amount of research and development work needs to be carried out in depth.
At present, an LED street lamp requires an average of 100 or so 1W white LEDs. The annual demand for street lamps in the country is 3 million baht. The annual demand for white light high-power LEDs will reach 300 million.
Lack of standard specifications cannot be fully promoted
Because LED street lights have two outstanding advantages: energy saving (reported to save more than 50% of electricity), long life (which can reduce maintenance and extend replacement time), the development and application of LED street lamps in China are developing rapidly. Many large and medium-sized cities have tried some LED street lights, but they have not been used in large quantities.
At present, the main problem of LED street lamps is that there is no standard specification, which cannot be fully promoted. Among them, several main parameters of LED for street lamps such as color temperature, color rendering (color rendering index) and glare have not been determined.
In addition, the price of LED street lamps is too high. At present, depending on the power and installation height, the price is between 3,000 yuan and 5,000 yuan per unit. It is difficult to promote and apply large areas.
The urban management system of street lamps is responsible for the long position, which brings great difficulties to the promotion and application of LED street lamps.
It is recommended that relevant departments organize the development of relevant standards for LED street lamps and establish relevant testing institutions as soon as possible.
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