Three major problems in the technical cost standard of large-scale commercial use of LED street lamps

Large-scale commercial use of LED street lights requires solving three major problems of technology, cost and standards

The application of LED (light-emitting diode) can be said to be everywhere. As a semiconductor light-emitting material, compared with other light-emitting materials, LED has the advantages of being green, efficient, reliable and durable, making other light-emitting materials pale in comparison. As the cost of high-power LEDs continues to decrease, it is possible to gradually replace traditional lamps. The application of LED light sources in road lighting has become a hot topic in the semiconductor lighting industry in recent years. What special technical requirements are there for the application of LED device products in street lamps? What are the advantages of LED street lamps compared with current ordinary street lamps? What are the shortcomings? How to solve them? Industry experts have explained from different aspects.

Formulating national standards is a powerful means of popularization and promotion

Li Jinmin, Director of the Institute of Semiconductors, Chinese Academy of Sciences

LED as a street light has the following advantages or features: high luminous efficiency, low reflection loss of lamps, energy saving of 70%; with digital brightness control function, it is more energy-saving; no high voltage is required, high safety; with software, the brightness can be automatically controlled remotely; it provides ultra-high brightness and high color rendering lighting sources in special circumstances such as accidents, foggy days, and rainy days; easy installation and maintenance; module installation, no redundant wiring; no light pollution or waste; long life, which means that it does not need to be replaced frequently, thus reducing the potential for traffic interruption and the maintenance costs paid for it. Someone has calculated that except for the higher cost per lamp and the initial installation cost than high-pressure sodium lamps, the use of LED street lights is much better than high-pressure sodium lamps in terms of laying cost, power consumption cost and life.

The main technical problems faced by LED street lamps are: output power and luminous flux, secondary optical design, heat dissipation design and power supply | voltage regulator system design. The improvement of output power and luminous flux also requires further improvement from the basic levels of epitaxial technology and chip technology of high-power white light LEDs. In terms of secondary optical design, the radiation forms of LEDs include Lambertian, side-emitting, bat-wing and concentrating types. In the field of road lighting, according to design experience, Lambertian and bat-wing types are more suitable. Through secondary optical design, the illumination range and photometric curve of LEDs meet the needs of road lighting. Heat dissipation is one of the key issues that LED street lamps need to solve. Due to the high brightness requirements and high heat generation of LED street lamps, and the harsh outdoor use environment, poor heat dissipation will directly lead to rapid aging of LEDs and reduced stability. In addition to the need for good heat dissipation of power-type LEDs themselves, since street lamps are used outdoors at night, the heat dissipation surface is located on the side, which is conducive to natural convection heat dissipation of air. The power supply system of LED street lamps is also different from that of traditional light sources. The low energy consumption and low operating voltage of LEDs are well matched with the low output power and low output voltage of solar cell modules. How to make a group of tightly compressed LEDs work safely and reliably is also an indicator for evaluating LED street lamps.

Based on the above analysis of the market prospects and technical issues of LED street lights, it can be seen that the factors affecting their application are:

First, the high cost of LED street lamps is not conducive to their popularization. Although the heat dissipation problem of LED street lamps has been initially solved, the high price and heavy lamp heads still hinder the popularization of LED street lamps.

Second, the reliability of the modularization of LED street lights still needs to be strengthened, as the failure of LED street lights may also be caused by reasons such as the driving circuit.

Third, LED street lamps, whether single-point or multi-point light sources, have the problem of heat dissipation. A street lamp using a 250W high-pressure sodium lamp, due to its mature technology and good heat dissipation control, has a small light decay even after working for 5,000 hours, and the luminous efficiency can reach more than 70%. With current technology, high-power LED street lamps under the same conditions have a large light decay and a luminous efficiency of 30% due to the difficulty in solving the heat dissipation problem. If you want to increase the light efficiency by increasing the voltage and current, it is easy to cause damage to the LED chip.

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, formulating national LED road lighting standards is also a very powerful means to popularize and promote LED street lights.

Heat dissipation and reliability are the main factors affecting applications

Chen Hesheng, Deputy General Manager of Jiangsu Wenrun Optoelectronics Co., Ltd.

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 of them, and the power supply design is complex. The other is to use high-power tubes as light sources, which are relatively expensive. Both methods inevitably take heat dissipation design and working reliability as the main design considerations. Domestically, they are mostly used in government demonstration projects, and there are few truly market-oriented projects. There are many application examples in this regard abroad, but their biggest disadvantages are still reliability, light lumens and price. Many projects do not show the advantages of long life well due to the poor quality of LEDs. In addition, from the perspective of cost and market, whether LED is used in combination with solar energy as a lighting source requires different design routes, and it cannot be completed by developing it as a light source alone.

When LED device products are applied to street lamps, the special technical requirements are mainly to design in combination with LED light intensity and light-emitting angle. In addition, due to the combination of multiple LEDs, the light output design must take into account the irradiation area, and the effectiveness of heat dissipation must be considered in the lamps.

The advantages of LED street lights over ordinary street lights are: energy saving, environmental protection, easy to adapt to low voltage, and can be directly matched with solar energy systems without the need for additional inversion and conversion processes, thus achieving maximum energy utilization.

Disadvantages: The lighting angle is small and uneven, the color rendering index is low, and the optical and heat dissipation designs are complex.

Technical deficiencies: The luminous flux under current technology is not enough, the luminous efficiency is too low, and the quality is difficult to guarantee.

Solution: The application of LED products in street lamps requires special design and special standards (using test data of traditional light sources to evaluate LED light sources is often not objective).

LEDs have inherent advantages and disadvantages in street lighting. The advantages are: first, as a point light source, if the design is reasonable, LED can directly solve the secondary light collection and light loss problems that traditional spherical light sources must rely on light emission to solve to a large extent; second, the uniformity of the light irradiation surface can be controlled, and in theory it can be completely uniform in the target area, which can also avoid the light waste in the "bright under the lamp" phenomenon of traditional light sources; third, the color temperature is optional, which is also an important way to improve efficiency and reduce costs in applications in different occasions; 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 still too high, the luminous flux is low, and the current price of LED light sources with the same illumination design is about 4 times that of traditional light sources (however, in street lamp products, the light source part does not account for a high proportion of the total cost, so the cost increase in engineering installation will not be too high, and there is still a lot of room for application), which is difficult to bear in civilian use. The current design and manufacturing standards are relatively chaotic, and the damage rate is high, which affects the life advantage of LEDs.

Suggestions: Unify LED standards, improve quality stability, establish a market competition coordination organization, avoid vicious competition, vigorously publicize the quality concept of LED, avoid being influenced by bad examples, make people accept that LED can actually achieve its advantage of long life, and improve the level of selecting and using LED.

The demand for white high-power LEDs will reach 300 million

Liang Bingwen, General Manager of Shanghai Lanbao Optoelectronic Materials Co., Ltd.

When LED devices are applied to street lamps, the special technical requirements are mainly reflected in the following two aspects: first, good luminous efficiency stability, which should not decay too quickly. Second, the consistency and maintainability of light color should be good, and the color of white light should not change due to long-term use. Both of these points require the overall heat dissipation of the lamp to be good and the optical design to be in place.

Compared with the current ordinary high-pressure sodium lamps, LED street lamps have the following advantages:

First, energy saving: At present, the luminous efficiency of white light LED is about 80lm/W, which can save 50% to 60% of electricity 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, high-power LED light sources can be used normally for 10 years without replacement, while traditional high-pressure sodium lamps need to be replaced every 1.5 years on average. The use of semiconductor light sources can greatly reduce maintenance costs.

Third, good color rendering: LED has a high color rendering index (75-80), people react quickly, the road looks brighter, feels more comfortable, and drivers feel safer. High-pressure sodium lamps have a narrow spectrum and poor color rendering (20-40), which makes them feel dim.

The main deficiencies are as follows:

First, the luminous efficiency is not high enough: although the luminous efficiency of laboratory-level high-power white light LEDs has exceeded 100lm/W, the luminous efficiency of mass-produced, cost-effective high-power white light LEDs is still around 60lm/W, and the energy-saving advantage has not been fully utilized.

Second, the ground has low reflectivity to LED light: Due to the current white light LED spectrum characteristics, the road surface and surrounding objects have low reflectivity to it, so the brightness of the road surface is low, compared with the yellow light of the sodium lamp, this is one of its weaknesses.

The current luminous efficiency of high-power white LED light sources is still at about 70lm/W to 80lm/W, and theoretically its luminous efficiency can reach about 300lm/W, so there is still a lot of room for development in technology. At the same time, semiconductor light source street lamps are currently in the initial stage of industrial development, and there is still a lot of room for improvement in improving heat dissipation efficiency, optimizing drive control systems, and light distribution design, and there is still a lot of research and development work to be carried out in depth.

At present, an LED street lamp requires an average of about 100 1W white light LEDs. Based on the annual demand for 3 million street lamps in the country, the annual demand for white light high-power LEDs will reach 300 million.

Lack of standards and specifications prevents full promotion

Peng Wanhua, Secretary General of Optoelectronic Devices Branch of China Optics and Optoelectronics Industry Association

Since LED street lamps have two outstanding advantages: energy saving (reportedly can save more than 50% of electricity) and long life (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 some roads trying out LED street lamps, but none of them have been adopted in large quantities.

The main problem with LED street lights at present is that there are no standards and specifications, and they cannot be fully promoted. Among them, several key parameters of LED street lights, such as color temperature, color rendering index (color rendering index) and glare, have not yet been determined.

In addition, the price of LED street lights is too high. Currently, the price ranges from 3,000 yuan to 5,000 yuan per unit, depending on the power and installation height, making it difficult to promote and apply them on a large scale.

The urban management system of street lamps is multi-party responsible, which brings great difficulties to the promotion and application of LED street lamps.

It is recommended that relevant departments organize the formulation of relevant standards for LED street lamps and establish relevant testing agencies as soon as possible.

The new street lamp design standard "Urban Road Lighting Design Standard" (CJJ45-2006) formulated by the Ministry of Construction came into effect on July 1, 2007, which did not mention the use of LED street lamps. Here, the relevant departments should organize relevant personnel to seriously discuss whether the use of LED street lamps can meet the above design standards or what supplementary revisions are needed as formal standard requirements.

In addition, it is necessary to formulate standards for road pavement testing methods for LED street lamps as soon as possible, formulate standards for LED street lamp fixtures (including LED lamps), propose requirements for the main parameters of LED street lamps, including color temperature, color rendering index, glare, luminous intensity (or illumination), angle, thermal resistance and reliability, formulate standards for LED street lamp fixture testing methods, and establish fair and authoritative LED street lamp related testing agencies.

We need to continuously improve the level of LED technology and reduce the cost of LED street lights. With the continuous breakthroughs in LED technology, especially the continuous improvement of LED luminous efficiency and the improvement of LED packaging and lamp design, the number of LEDs and other components used can be reduced, which can greatly reduce the cost of LED street lights.

It is hoped that the management of street lights on urban roads can be unified by one department, so that the promotion of LED street lights will be smoother.

High initial installation cost restricts promotion and application

Shao Jiaping, Technical Manager of Huagang Optoelectronics (Shanghai) Co., Ltd.

The initial installation cost of LED street lights is still 2-3 times that of traditional high-pressure sodium lamps and metal halide lamps. This is because the current LED light source cost is relatively high and requires more complex optical, thermal and drive designs.

However, in the past one or two years, a large number of application cases of LED street lamps have appeared both at home and abroad. Its main advantages are: long life and high overall luminous efficiency of lamps, thus achieving overall energy saving effect in operation.

The LED light source itself has a lot of room for improvement in light efficiency. The characteristics of semiconductor technology make it possible to double the light efficiency (corresponding external quantum efficiency) on the existing basis. At present, the top level of high-power LED light efficiency in the industry is 100lm/W, and the research and development level is greater than 130lm/W, and it is expected to reach a level greater than 200lm/W in the future. LED light sources are green and environmentally friendly, do not contain heavy metals such as mercury, and are more convenient for recycling. LED light source systems are easy to maintain, with low overall operating costs and high product quality. The above advantages make the market prospects of LED street lights widely optimistic.

LEDs are essentially point light sources in lighting applications, so their optical design, including the design of primary lenses or reflective devices and the design of secondary optics, is a major application difficulty.

In addition, the heat dissipation solutions of LED street lighting systems, such as the integrated design based on the metal shell, auxiliary heat dissipation devices such as fans and heat pipes, and effective dust prevention (dust will greatly hinder heat dissipation), are all areas that require special attention compared to traditional street lights.

In addition, the constant current driving power supply required by LED is a cornerstone to ensure its normal operation. The simple switching power supply solution often causes damage to LED devices. Therefore, the further promotion of LED street lights depends on the increasing maturity of the overall solution of light, heat, electricity and other aspects.

The large-scale application market will start in 2010

Fang Zhilie, Professor of Fudan University

At present, the street lamp application market has started, for five reasons. First, under the condition of intermediate vision, the sodium lamp currently used in street lamps is 30% less efficient than the efficiency measured under the condition of bright vision. However, LED has a full spectrum efficiency that can be increased by 40%. Currently, replacing sodium lamps can save 30-40% of electricity, which is in line with the national policy of saving electricity and reducing emissions. Second, considering the long life, maintenance costs can be avoided. Due to the small driving current, the cost of cables, transformers and engineering is also reduced. Third, the visual perception and resolution under white light are improved. Fourth, due to the low power consumption and low driving voltage, it can be combined with photovoltaic cells to form a solar street lamp. Fifth, street lamps are all built and managed by government departments, which is easier to promote.

At present, many cities and even small towns have street lamp demonstration projects, with dozens of lamps at least and tens of thousands at most. There are already many orders for 20,000 street lamps in China. It can be said that this is a dark horse in general lighting. With the further improvement of efficiency and the improvement of technology, it will develop rapidly. Considering that there are about 200 million street lamps in my country, this vast market should be paid special attention to. In addition, some enterprises have already exported their products, and the market prospects are more promising. In 2010, the large-scale application market will be launched.

At present, the products are in the initial stage, with good and bad products. The main problem is that the heat dissipation problem is not solved well, which not only reduces the luminous efficiency, but also causes serious light decay problems, or even failure. The relevant departments should speed up the formulation of standards, conduct light decay tests before leaving the factory, reduce the thermal resistance of lamps, fully dissipate heat, and truly achieve high efficiency and long life, so as to facilitate the cultivation and healthy development of the market.

LED replaces high pressure sodium lamp and saves 40%

Chris James, Vice President of Marketing at Cree

LED performance has now surpassed the commonly used fluorescent lamps, and it is foreseeable that LED lighting technology will enter a variety of environments. In addition to energy saving, LED lamps have a much longer service life than traditional bulbs, and do not use harmful substances such as mercury, mercury, and lead commonly found in ordinary bulbs, making LED lamps more environmentally friendly.

The LED City Lighting Action (LEDCity Community) was launched in February 2007 to promote a parking garage lighting pilot project in Raleigh, North Carolina, with the support of Cree, Lighting Science Group, AmTech Lighting Services and Progress Energy. The goal of the community is to encourage cities to strengthen cooperation and improve efficiency when deploying energy-saving lighting so as to achieve cost savings and environmental protection as soon as possible. The pilot project is to replace high-pressure sodium lamps with LED lamps. According to Progress Energy's evaluation, the energy saving effect is 40%.

LED city lighting initiatives are designed to meet local needs. From Texas in the United States to Toronto in Canada, LED lighting has been successfully deployed throughout North America, with each demonstration area bringing huge energy savings to the local area and meeting its economic needs. For example, the city of Arnold, Michigan, where the University of Michigan is located, has a population of 125,000 and recently installed more than 1,000 LED streetlights. This may seem like a small number in China, but it is of great significance to a US city of the size of Arnold. Each 56-watt LED lamp can be used continuously for 10 years, replacing a 120-watt bulb with a service life of only two years, which has halved the city's public lighting energy consumption and reduced greenhouse gas emissions by 2,425 tons per year, which is equivalent to the amount of exhaust emissions from 400 cars on the road for a year.

Cree, with the help of LEDCity partners such as Tianjin Economic and Technological Development Zone, is promoting this transformation as an advocate of the new generation of lighting. The application of energy-saving and environmentally friendly LED technology will help solve the world's energy shortage problem and is one of the most effective energy-saving measures we can take so far.