What Is an LED Street Light?

LED street light refers to the street light made with LED light source, which has the unique advantages of high efficiency, safety, energy saving, environmental protection, long life, fast response speed, high color rendering index, etc., and is of great significance for energy saving in urban lighting.

LED street light

LED street light refers to the street light made with LED light source, which has the unique advantages of high efficiency, safety, energy saving, environmental protection, long life, fast response speed, high color rendering index, etc., and is of great significance for energy saving in urban lighting.

Chinese name

LED street light

Foreign name

LED LAMP FOR ROAD LIGHTING

Advantages

Environmental protection, low power consumption, high light efficiency, long life

Features

Unidirectional light

LED street lights are different from conventional street lights,

1. The biggest feature of lighting LEDs is that they have the function of directional light emission, because almost all power LEDs are equipped with reflectors, and the efficiency of such reflectors is significantly higher than that of lamps. In addition, the efficiency of the self-reflector has been included in the light effect detection of the LED. Road lamps using LEDs should make full use of the characteristics of the directional light emission of LEDs, so that each LED in the road lamps can directly direct the light to various areas of the road surface, and then use the auxiliary light distribution of the lamp reflector to achieve Very reasonable comprehensive light distribution for road lamps. It should be said that road lamps must truly meet the illuminance and uniformity requirements of CJJ45-2006 and CIE31 and CIE115 standards, and the luminaire should include the function of three-time light distribution to achieve better. , And the LED with a reflector and a reasonable beam output angle itself has a good primary light distribution function. In the lamp, the installation position of each LED and the direction of the emitted light can be designed according to the height of the road lamp and the width of the road surface to achieve a good secondary light distribution function. The reflector in this type of luminaire is only used as an auxiliary three-time light distribution means to ensure better uniformity of road illumination.

On the actual road

Assume that there are three sections of roads in a city with lengths of 3 kilometers, 5 kilometers, and 10 kilometers, and street lamps are laid at intervals of 30 meters and one on each side. The total number of street lamps required for these three sections is 202 and 334, respectively. , 668, traditional street lights are based on 250W high-pressure sodium lamps, LED street lights are based on 50W power for comparison.

The unit price of traditional street lamps is 1,000 yuan per lamp, and the unit price of LED street lamps is 3,000 yuan. The cost of light sources for paving the three lengths of traditional street lamps is 202 * 1000 = 202,000 yuan, 334 * 1000 = 334,000 yuan, 668 * 1000 = 668,000 yuan. The cost of light sources required to lay three lengths of LED street lights is: 202 * 3000 = 606,000 yuan, 334 * 3000 = 1.002 million yuan, and 668 * 3000 = 2.004 million yuan.

Let's analyze the cost of laying cables with two light sources on a three-segment road. The cable load flow of a traditional street light trunk line on a 3 km road I = P / U = 202 * 250/220 = 230A. It requires a copper core with a cross-sectional area of 60mm2 The unit price of the cable is 120 yuan / meter, the cable cost is 120 * 3000 = 360,000 yuan, the load flow of the LED street light trunk cable l = P / U = 202 * 50/220 = 44A, and its cross-sectional area is 10mm2 Copper core cable, it needs a copper core cable with a cross-section of 12mm2, the unit price is 12 yuan / meter, the cable cost is 12 * 300 = 36,000 yuan, the load flow of the traditional street lamp trunk cable on a 5km road I = P / U = 333 * 250/220 = 377A, which requires a copper core cable with a cross-section of 90mm2, the unit price is 180 yuan / meter, the cable cost is 980 * 5000 = 900,000 yuan, the load flow of the LED street lamp trunk cable I = P / U = 333 * 50/220 = 73A, which requires a copper core cable with a cross-section of 20mm2, the unit price is 25 yuan / piece, the cost is 25 * 5000, 125,000 yuan, and the cable flow of a 10 km road traditional street light trunk line I = P / U = 666 * 250/220 = 680A, it needs a copper core cable with a cross section of 400m2, the unit price is 360 yuan / meter, the cable cost is 360 * 10000 = 3.6 million yuan, and the load flow of the LED street lamp trunk line cable I = P / U = 666 * 50220 = 1 46A, it needs 42mm2 copper core cable in cross section, the unit price is 60 yuan / meter, and the cost is 600,000 yuan.

In order to play a supporting role in science and technology, promote stable and rapid economic development, focus on breaking through key and critical technologies, promote energy conservation and emission reduction, effectively guide the healthy and rapid development of China's semiconductor lighting applications, expand the size of the semiconductor lighting market, drive consumer demand, and promote the core of the industry The improvement of technological research and development and innovation capabilities has rapidly improved the overall competitiveness of China's semiconductor lighting industry. After research by the Ministry of Science and Technology, it was agreed to be in Tianjin, Shijiazhuang, Baoding, Hebei, Liaoning, Harbin, Heilongjiang, Shanghai, and Yangzhou. 21 cities including Ningbo City, Ningbo City, Fuzhou City, Fujian Province, Xiamen City, Fujian Province, Jiangxi Province, Weifang City, Shandong Province, Zhengzhou City, Wuhan City, Guangdong Province, Hainan Province, Sichuan Province, Mianyang City, Sichuan Province, and Shaanxi Province Semiconductor lighting application engineering (referred to as "ten cities and ten thousand") on a trial basis.

The design of traditional LED street lights mainly focuses on the number of lumens of LEDs, while less attention is paid to the heat dissipation. In fact, the number of LED lumens is rapidly increasing. In 2009, the number of single-watt lumens of mass-produced LEDs has reached 100 lumens, and this value is still growing rapidly. The corresponding theoretical system of heat transfer is mature, and the heat transfer methods that we can use are basically clear: conduction, convection, radiation, and phase change heat transfer. Therefore, in terms of heat transfer or heat dissipation, the measures we can take are visible and limited.

The heat dissipation technology of LED street lamps generally uses a heat-conducting plate method. It is a 5mm-thick copper plate. In fact, it is a uniform temperature plate, which evenly heats down the heat source. There are also heat sinks for heat dissipation, but the weight is too large. Weight is very important on the street light system, because the street light is 9 meters high, if it is too heavy, the danger will increase, especially when encountering

To solve these existing problems, it is recommended that street light manufacturers start with basic materials and solve the problem of high-power LED heat sources from the inside out. For example, when bonding light-emitting components to aluminum substrates, thermal conductive adhesives play a key role. Some manufacturers think that the thermal conductivity of thermal conductive films or thermal pads is better, and the thicker the film, the better, but they do not think about thermal resistance. No matter how good the thermal conductivity is, the thermal resistance to the film thickness is useless. What's more, the thermally conductive adhesive film or soft thermally conductive pad cannot really adhere to the substrate, and there are actually many pores on the bonding surface. These pores, viewed under an electron microscope, are like hollow air pockets, which is another form of thermal resistance. In the presence of so many thermal resistances that interfere with heat conduction, the efficiency of heat dissipation and heat conduction is virtually reduced.

For low thermal resistance, use thermal conductive adhesive. Soft ceramic thermal conductive adhesive for screen printing is recommended. The soft ceramic thermal conductive adhesive for screen printing is different from the traditional laminating thermal conductive adhesive film. The soft ceramic thermal conductive adhesive is a soft semi-liquid. When the screen printer blade is coated on an aluminum substrate, the thermal conductive particles will penetrate the pores on the surface of the substrate and I fill it to full. In this way, a completely flat surface with no pores will be formed, which will be completely tightly bonded to the LED epitaxial substrate. In this way, the thermal resistance is reduced to a minimum, and the heat can be quickly conducted out, which naturally reduces the ambient temperature of the LED die, prolongs the life of the epitaxy, and significantly delays the occurrence of light decay. In addition, due to the ductility of the soft ceramic heat-conducting paint for screen printing, it will change with the thermal expansion and contraction of the aluminum substrate during high temperature baking or reflow. The stress is very small, and it will not cause the aluminum substrate to warp, let alone Will burst.

For the external protection of LED lamps, it is recommended to use soft ceramic heat sink paint for LED lamps. This spray-type soft ceramic heat-dissipating paint can be directly sprayed on the outside of the LED lamp. The construction operation is simple, it can adapt to various shapes of heat-dissipating structures, and it can also be adjusted to different colors to meet the needs of landscape design. The soft ceramic particles in the spray-type heat-dissipating paint are nano-processed. The fine particles are not only easy to spray gun operation, but also make the thermally conductive particles on the same coating area more and denser, and the area where the temperature is volatile and diffused becomes larger. Let the heat of the LED luminaire be conducted quickly. Soft ceramic heat-dissipating paint is a thermosetting material, which complies with RoHS environmental protection and safety regulations. The construction procedure is simple and does not require any special equipment. After curing, it can be cured for a long time without the problem of high temperature. LED street lights for outdoor use,

As the most noticeable new generation light source in the world, LED is known as the most promising green lighting source in the 21st century due to its high brightness, low heat, short life, non-toxic, recyclable and other advantages.

Since the birth of the first red light-emitting semiconductor light-emitting diode in 1962, people have continuously developed a variety of monochromatic LEDs such as orange, yellow, and green, and have been used for various signal instructions, signs, digital displays, and gradually developed into small LED display screens, etc. . It uses a solid semiconductor chip as a light-emitting material. When excess energy is emitted, photons are emitted, and LEDs made of semiconductor PN junction light-emitting sources can be produced. They were introduced in the early 1960s. Red light-emitting diodes were first developed in 1964. The LED appears.

The world's first commercial light-emitting diode (LED) was made from germanium in 1965, and its unit price was $ 45. Soon after, Monsanto and Hewlett-Packard successively introduced commercial LEDs made of GaAsP materials. This is much lower than the 151m of general 60 100W incandescent lamps. In 1991, the industry used MOCVD epitaxial growth quaternary materials to develop high-brightness light-emitting diodes; in 1994, the first blue light-emitting diode was developed on a GaN substrate; 1997 In 2014, the first white LED was made by exciting the phosphor with blue light; in 2001, the white LED was made by exciting the phosphor with ultraviolet light.

1. The global industrial structure is monopolized, mainly in Japan and Taiwan.

The semiconductor lighting industry has formed a three-legged industry distribution and competition pattern dominated by the three major regions of Asia, the United States and Europe. The global LED industry is mainly located in Japan and Taiwan. Among them, Japan accounts for nearly 50% of the global LED output value; Taiwan (including Taiwan and mainland factories) LED output value 2 accounts for 21% of the global LED output value ranked second.

2. International big factories lead the industrial development and take advantage of technology to occupy the production of high value-added products.

Companies in Japan and the United States take advantage of their innovative advantages in new products and technologies, and are mainly engaged in the production of the highest value-added products. Among them, Japan almost monopolizes the global high-end blue and green LED market, and is the second largest production area and the largest output value in the world.

3. Industrial investment continued to increase, and the pace of cooperation between well-known international manufacturers accelerated to occupy a favorable market position.

Fourth, China has become an important packaging base, and companies at home and abroad have invested to seize the huge domestic market.

1. There are many LED street lights in China

In response to the global financial turmoil, the Central Development and Reform Commission has provided 4 trillion yuan with local financial support. It is estimated that more than 10 trillion yuan will be invested in national transportation, supporting enterprises, and improving infrastructure. The Ministry of Science and Technology of the People's Republic of China has launched the "Ten Cities, Ten Thousands" LED street lamp semiconductor lighting application project. Under this strong east wind, the semiconductor lighting industry that has always been supported by the government will be a great opportunity for development. Many companies are optimistic about the development space of this rising industry, especially the obvious energy-saving advantages of semiconductor outdoor lighting. In the past two years, many companies have put into production. Without knowing the characteristics of semiconductor road lighting production, they have simulated, imitated, and made along the shape of today's conventional lighting street lights, and their products have been introduced to the market. Most products have problems to varying degrees.

Second, domestic light sources can not meet market demand

The development of domestic LED light sources started relatively late relative to foreign countries, and the technical level is still a certain distance from the leading international players. Although the theoretical life of domestic LED light sources can reach 100,000 hours, the heat dissipation problem cannot be completely and effectively solved, so that its actual life Great discount; unstable power system: LED drive power is unstable is the industry consensus, in fact it is dragging the back of the LED lighting industry, because the drive power is an important part of LED street lights, its failure will cause the entire lamp to fail. The poor reliability of the power supply causes the installed street light to be broken in a short period of time. This is difficult for outdoor high-level devices such as LED street lights to install and more difficult to repair. For street light manufacturers, unstable power supplies make maintenance costs more difficult. Climb up.

3. Difficult product maintenance and higher product prices

Maintenance issues. The high pressure sodium lamp is easy to maintain, as long as the lamp is scrubbed and does not need to be replaced, the light source is replaced once every 4 years, which is very convenient. The LED street light involves LED tubes, modules (including lenses, etc.), power supply devices, etc. The possibility of damage to components and components is large, maintenance is difficult, and it is likely to be replaced as a whole, which costs more. High prices: LED street lights are 2-5 times more expensive than high-pressure sodium lamps. Even though the power consumption of LED street lights is only one-half of that of high-pressure sodium lamps, but because the price is much higher than high-pressure sodium lamps, the cost of using high-temperature sodium lamps instead of LEDs is recovered The cycle will still be long;

4. There are problems in product design and quality, which need to be improved

The color of LED street lights. High-power LED street light, as a road lighting source, is too cold or even gloomy in visual sense, which is not conducive to motor vehicle driving. The life of LED street lights is not high. The average life of high-pressure sodium lamps is 4 years. There is no practical experience about the service life of LED street lights. The existing enterprises claim 50,000 hours, and there is no reliable basis. Because the life of the capacitor of the LED driving circuit device is only about 10,000 hours.

High-power LED street lights basically use white light with a color temperature of around 5000K. As a light source for road lighting, the visual sense is too shady, and at the same time, the observation ability will decrease during hyperopia. In this regard, the street light users have the most say. Yellow or warm white light around 3000K is more suitable for road lighting. Therefore, daylight-colored LED street lights Not suitable for street lights.

LED street lights lack uniform technical standards in terms of product specifications. There is no uniform LED street light production technology standard. Each manufacturer produces its own products according to its own standards. It is difficult to universalize each other. In addition, LED street light manufacturers In a system, the light source and electrical appliances are bundled with the lamps, and their different working characteristics are difficult to maintain. The original products must be used for maintenance.

LED street lights are mainly used for road lighting such as main roads, secondary roads, branch roads, factories, schools, gardens, city squares, and courtyards.

The improvement of output power and luminous flux also needs to be further improved from the basic levels such as epitaxial technology and chip technology of high-power white LEDs. In terms of secondary optical design, the radiation forms of LEDs are Lambertian, side-fired, bat-wing, and condensing. 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 are in line with the needs of road lighting.

The most common form of LED used in road luminaires is mainly in the luminaire. Matrix-type LEDs are installed on an almost flat mounting surface (also a reflective surface). This design method is not possible to obtain a good luminaire. Light distribution.

The technology is becoming more and more mature, and the efficiency of the light source has reached above 100lm / W, which has made it possible for energy-saving transformation of urban street lighting. LED street lights, especially high-power LED street lights, are hitting the traditional street light market at a rapid speed.

High-power LED street lights, as the name suggests, are street lights with a power of more than 30 watts and using new LED semiconductor light sources. The standard is the uniformity of road illumination, which conforms to road illumination. (Actually, the 1/2 center light spot reaches 25LUX, the 1/4 center light intensity reaches 15LUX, the minimum light intensity of 16 meters is 4LUX, and the overlapping light intensity is about 6LUX. It refers to LED street lights using solar silicon panels as the power supply.

With the country's emphasis on energy saving and emission reduction and the urgency of energy saving transformation, Guangdong Province will also vigorously promote LED street lamps, but the LED street lamp scheme promoted by Guangdong Province is widely questioned. The reason is that there are many problems with LED street light products, such as: light decay, heat dissipation, and lighting ability.

Energy saving but insufficient light

Energy saving is the energy saved under the same average illuminance. This average illuminance cannot be just the average illuminance on the ground! The light intensity of the space has a good pre-judgment for vehicles coming from a distance to prevent traffic accidents! But domestic installation LED street lights are sacrificing light to achieve energy savings.

Heat dissipation of LED street lights

The street lamp is used outdoors. To be waterproof and dustproof, the lamp must be sealed. The temperature of the water vapor inside the lamp exceeds 100 degrees under extreme weather conditions. The LED continuously works in such a high temperature environment. If done well, the lamp will be extremely easy to break or the light decay is serious. The heat dissipation problem of domestic high-power LED street lights has not been completely solved, and the subsequent maintenance costs of the product must increase.

LED light penetrability

On rainy days and foggy days, LED lights are not capable of penetrating fog.

Easy to attract mosquitoes outdoors

Because mosquitoes especially like light of certain wavelengths of LED lights, there is a moth fluttering phenomenon, which will affect its light efficiency.

In summary: As a new light source, LEDs have irreplaceable advantages in replacing incandescent lamps and fluorescent lamps, but there are still some problems with the use of high-power LED street lamps. The promotion of radical comprehensive replacement of LED street lights (especially the main road) may cause sequelae. If it encounters extreme weather, it may cause a large number of bad lights or severe light decay, affecting road safety.

LED street light power supply lightning protection design

There are four main types of lightning strikes:
1. Direct strike lightning Direct strike lightning contains great energy, and the lightning current with a peak voltage of up to 5000kv goes into the ground, which has great destructive power. Has three effects:
(1) A huge rich current flows to the ground within a few microseconds, causing the ground potential to quickly pick up, causing a counterattack accident and endangering human and equipment safety.
(2) The lightning current generates strong electromagnetic waves, and induces extremely high pulse voltages on the power and signal lines.
(3) Lightning current flowing through electrical equipment generates extremely high heat, which can cause a fire or explosion accident.
2. Conducted by lightning, the lightning strikes the line or the extremely high voltage generated by electromagnetic induction is transmitted from the outdoor power line and communication line to the electrical equipment inside the building.
3. Frequent discharges between induced thundercloud layers generate strong electromagnetic waves that cause common-mode and differential-mode interference, affecting the operation of electrical equipment.
4. Switching over-voltage power supply system to turn on or off the inductive and capacitive loads, short-to-ground, short-circuit of the power line, etc., can generate high voltage pulses on the power line, the pulse voltage can reach 3 to 5 times the normal voltage , Can seriously damage the equipment. The damage effect is similar to a lightning strike.
The most effective way to prevent street lights from being damaged by lightning:
1. Combination of external lightning protection and internal lightning protection Generally, the exterior of LED street lights is a conductive material, which itself is equivalent to a lightning rod. The design must install down-conductors and ground networks. These systems constitute an external lightning protection system. This system can avoid fire and personal safety accidents caused by direct strike of LED street lights. The internal lightning protection system refers to the equipment inside the street light is protected by grounding and voltage protection. This system can prevent inductive lightning and other forms of overvoltage from invading, causing power supply damage, which cannot be guaranteed by external lightning protection systems. The two are complementary and complementary. The internal lightning protection system must be connected to an external lightning protection system or an overvoltage protector and equipotentially connected to many components, such as housings, cables entering and exiting the protection zone, and metal pipes.
2. Lightning protection equipotential connection In order to completely eliminate the destructive potential difference caused by lightning, power lines, signal lines, metal pipes, etc. must be equipotentially connected with an overvoltage protector, and the interface of each inner protection zone must also be For local equipotential bonding, each local equipotential connection should be connected to each other, and finally to the main equipotential connection.
3. Set up lightning protection zone LED street lights. In addition to the power supply equipment, some communication equipment will be set up to control the switching and brightness of the street lights. These devices and power supplies need to be placed in the lightning protection zone, and the protection area is directly shielded by the shell. The electromagnetic field is much weaker here.
4. High-quality protection equipment-Lightning protection module and overvoltage protection module Lightning protection device is used to connect the protected system to the equipotential system in the shortest time (nanosecond level), so that all ports of the equipment are equipotential. At the same time, the huge pulse energy generated by the lightning in the circuit is released to the ground through the short-circuit line, which reduces the potential difference between the interface ends of the device, thereby protecting the device.

LED street light inspection program

The LED street light power module must not only be designed in accordance with the above requirements, but also must pass strict inspection procedures:
1. Control devices with constant voltage output function or constant current output function or both functions shall be inspected using GB19510.12 / IEC61347-2-13 safety standards.
2. For control devices that only have the function of controlling the logical changes of LED light, dark, flashing, color, etc., the safety standard GB19510.12 / IEC61347-2-11 should be used for inspection.
3. If a control device has both of the above functions, it should be inspected in accordance with GB19510.12 / IEC61347-2-13 safety standards.
Practice has proved that after scientific design and strict inspection, not only can it ensure that the LED street light system is not harmed by lightning, but also eliminate the common mode and differential mode interference of lightning on power supply equipment.