What is LED street light

Road lighting is an important part of urban lighting. Traditional street lamps are often used. High-pressure sodium lamps emit 360 degrees. The disadvantage of large light loss has caused a huge waste of energy. At present, the global environment is deteriorating, and all countries are developing clean energy. With the rapid growth of the national economy, the contradiction between energy supply and demand in China has become increasingly prominent, and there has been a serious shortage of power supply. Energy conservation is an urgent problem that needs to be resolved. Therefore, the development of new high-efficiency, energy-saving, long-life, high color rendering index, environmentally friendly LED street lights is of great significance for energy saving in urban lighting.

With the acceleration of China’s urbanization process, LED street lights have gradually entered people’s field of vision with the advantages of directional light emission, low power consumption, good driving characteristics, fast response speed, high shock resistance, long service life, and environmental protection. A new generation of energy-saving light sources with the advantage of replacing traditional light sources. Therefore, LED street lights will become the best choice for energy-saving reconstruction of road lighting.

LED street lights (Light Emitting Diode, light-emitting diodes) are semiconductor lighting. It is a high-efficiency solid-state light source based on a semiconductor PN junction that can emit light with weak electrical energy. Under a certain forward bias voltage and injection current, the holes injected into the P region and the electrons injected into the N region are diffused to After the active area is recombined by radiation to emit photons, the electrical energy is directly converted into light energy. It is a solid-state cold light source with the characteristics of environmental protection, no pollution, low power consumption, high light efficiency, and long life. Therefore, LED street lights will become the best choice for energy-saving retrofit of road lighting.

The main occasion of LED street light

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.

Features of LED street light

The difference between LED street lights and conventional high-pressure sodium lamps is that the light source of high-power LED street lights uses low-voltage DC power supply and a high-efficiency white light diode composed of blue LEDs and yellow phosphors. The unique advantages of high color rendering index can be widely used in urban road lighting temperature up to 135 degrees. Low temperature resistance -45 degrees

1.Unidirectional light, without light radiation, ensuring light efficiency;

2.The LED street light has a unique secondary optical design, which illuminates the light of the LED street light to the area to be illuminated, which further improves the lighting efficiency to achieve the purpose of energy saving;

3. LED light source efficiency has reached 90-110lm / W, and there is still much room for development, the theoretical value of 250lm / W. The luminous efficiency of high-pressure sodium lamps only increases with the increase of power. Therefore, the overall light-efficiency LED street lights are stronger than high-pressure sodium lamps. 4. The color rendering of LED street lamps is much higher than that of high-pressure sodium lamps. The color rendering index of high-pressure sodium lamps is only about 23, and the color rendering index of LED street lamps is above 75.

4.The light decay of LED street lamps is small, less than 3% in one year, and it still meets the requirements of road use illumination for 10 years, while the high-pressure sodium light decays, and it has fallen by more than 30% in about one year. Designed to use lower power than HPS;

5.LED street lights have automatic control energy-saving devices, which can achieve the maximum possible reduction in power and energy savings when meeting lighting requirements at different times.

6.LED is a low-voltage device. The voltage for driving a single LED is a safe voltage. The power of a single LED in a series of products is 1 watt, so it is a safer power source than using a high-voltage power supply. It is especially suitable for public places (such as street lamps). Lighting, factory lighting, automotive lighting, civil lighting, etc.)

7.Each unit LED chip has only a small volume, so it can be prepared into various shapes of devices, and is suitable for variable environments.

8. long life: can be used for more than 50,000 hours, providing three years of quality assurance. The disadvantage is that the life of the power supply is not guaranteed.

9.Easy installation: no need to bury cables or rectifiers, directly connect to the lamp pole or nest the light source into the original lamp housing.

10.Excellent heat dissipation control: In summer, the temperature is controlled below 45 degrees, and passive cooling is adopted, so the heat dissipation guarantee in summer is insufficient.

11.Reliable quality: All circuit power supplies use high-quality components, and each LED has separate overcurrent protection, so there is no need to worry about damage.

12.Uniform light color: No lens is added, and uniform light color is not sacrificed to improve brightness, thereby ensuring uniform light color without aperture.

13.LED does not contain harmful metal mercury, which will cause harm to the environment when scrapped.

14.LED street lights have automatic control energy-saving devices, which can achieve the maximum possible reduction in power and energy savings when meeting lighting requirements at different times. Humanized functions such as computer dimming, time-phase control, light control, temperature control, and automatic inspection can be realized.

What to pay attention to when installing street lights

LED street light power system

The power supply system of LED street lights is also different from traditional light sources. The constant current drive power required by LEDs is a cornerstone to ensure its normal operation. Simple switching power supply solutions often cause damage to LED devices. How to make a tightly packed set of LEDs safe is also an indicator for examining LED street lights. The requirement of LED for the driving circuit is to ensure the characteristics of constant current output. Because the relative change area of the junction voltage is small when the LED is working in the forward direction, ensuring the constant LED driving current also basically ensures the constant LED output power. For the current situation of unstable power supply voltage in our country, it is very necessary for the driving circuit of road lamp LED to have constant current output characteristic, which can ensure the constant light output and prevent the LED from over-power operation. The active electronic switch circuit or the high-frequency current is used to drive the LED. The above two schemes can make the driving circuit have a high conversion efficiency while maintaining a good constant current output characteristic.

LED Power

LED power supplies are switching power supplies. The quality and reliability of a switching power supply depends on its circuit design, production process, and device quality. Electrolytic capacitors are an essential part of high-power switching power supplies. The normal working life of a switching power supply depends on the life of the electrolytic capacitor used by the power supply. The life of the electrolytic capacitor depends on the life of the capacitor itself and the operating temperature. The operating life of the electrolytic capacitor varies greatly at different temperatures. The impact resistance of LED is relatively poor, so it is necessary to strengthen the protection in this regard. Especially for some products installed outdoors, the start and stop of the grid load and lightning strikes will impact the power supply. Therefore, the input end of the LED driving power supply must have a protection circuit to suppress the surge to prevent the switch from damaging the LED momentarily. Due to the different environments in different places, we must focus on the environment of the LED lighting workplace, such as temperature, humidity, and installation location. Considering the working mode of the power supply, if no soft-start circuit is added, the output will have a voltage spike immediately after power-on. In order to better protect the LED, a soft-start circuit is needed. This is a key factor in driving power stability.

LED drive power design

1.LED current size Everyone knows that if the LED ripple is too large, the life of the LED will be affected, and how much the impact is, but there is no specific index at present.

2.Chip heating This is mainly for the high-voltage driver chip with built-in power modulator to reduce the power consumption of the chip. Do not introduce additional power consumption and do a good job of heat dissipation.

3.Power tube heating The power consumption of the power tube is divided into two parts, switching loss and conduction loss. For LED mains driving applications, the switching damage is much greater than the conduction loss. The switching loss is related to the cgd and cgs of the power tube and the driving ability and operating frequency of the chip, so to solve the heat generation of the power tube can be solved from the following aspects: A. The MOS power tube cannot be selected based on the on-resistance, because The smaller the internal resistance, the greater the capacitance of cgs and cgd. B. The rest is the frequency and chip driving capability. The frequency is also proportional to the conduction loss, so when the power tube heats up, you must first think about whether the frequency selection is a bit high. When the frequency is reduced, in order to obtain the same load capacity, the peak current must be larger or the inductance also larger, which may cause the inductor to enter the saturation region. If the inductor saturation current is large enough, you can consider changing the CCM (continuous current mode) to DCM (discontinuous current mode), so you need to add a load capacitor.

4.Frequency reduction The frequency reduction is mainly caused by two aspects. The ratio of input voltage to load voltage is small, and the system interference is large. For the former, be careful not to set the load voltage too high, although the load voltage is high, the efficiency will be high. For the latter, you can try the following aspects: a. Set the minimum current point again; b. Clean the wiring, especially the critical path of sense; c. Select the small point of the inductor or use a closed magnetic circuit inductor ; D, add RC low-pass filtering, this effect is a bit bad, the consistency of C is not good, the deviation is a bit large, but it should be enough for lighting.

5.Inductor or transformer selection.Given that the working voltage of high-power light-emitting diodes is only 3V, 220V AC is converted into DC power through full-bridge rectification. The utilization efficiency is only 60%. More than three light-emitting diodes must be connected in series to make the total power utilization efficiency exceed 80%. According to the principle of 3 primary colors to synthesize white light, three red, green, and blue 1W high-power light-emitting diodes are connected in series to work, and the brightness equivalent to 3W white-emitting LED can be obtained. At the same time, six kinds of colored light can be combined to meet people’s preference for changing colored light. According to the power consumption characteristics of the power grid, the requirements of LED characteristics, and related LED products, the following points must be considered when selecting LED driving power:

a）According to LED current and voltage characteristics, it is ideal to use constant current drive. It can avoid the current change caused by the change of LED forward voltage, and the constant current makes the brightness of the LED stable.

b)In addition, the LED luminous flux is inversely proportional to the temperature, so the power supply should be minimized and a well-designed cooling system should be used during use. Thereby reducing the ambient temperature at which the LED operates.

c)In order to ensure the overall life of the LED product, the junction temperature of the LED must be controlled within a certain range, that is, the working environment temperature of the LED product must be controlled.

d) High-reliability LED products are mainly composed of LED chips and power supply, heat dissipation shell, control circuit and so on. The quality of the LED power supply directly affects the quality of the product. In particular, LED street light products are installed at high altitudes, making maintenance inconvenient and expensive.

e) LEDs are energy-saving products, and the drive power must also meet the requirements of energy-saving. Especially the structure in which the power supply is installed in the luminaire is particularly important. Because the luminous efficiency of the LED decreases as the temperature of the LED increases. The efficiency of the power supply is high, its power consumption is small, the heat generation in the lamp is small, and the temperature rise of the lamp is reduced. It is beneficial to delay the light decay of LED. 3 Constant current drive mode In order to match the volt-ampere characteristics of LEDs, LED power supplies must use a constant current drive mode.

How to control the LED power switch

Generally, it is divided by road sections. As long as there is a street light, there will be a street light control box, which is equipped with a fixed clock for switching lights. However, this fixed clock cannot change the time of switching lights according to the weather. eliminated. Nowadays, it is generally an automatic control system for street lights. By combining time control and light control, the light intensity of the switch lights is reached within the time range of sunset and sunrise, and the system will automatically send instructions to the street light control box on each road. Street light switch operation.

Design of multi-functional LED street light control system unit controller. Aiming at the problems existing in the use of traditional street light control systems, a design scheme of an LED street light control system is proposed which uses a single chip microcomputer as the control core and is composed of RS485 communication, photoelectric detection of object movement, and PWM modulation constant current drive module. The control system is mainly composed of a unit controller and a branch controller. The unit controller has functions such as moving object detection, ambient light detection, street light driving, and fault detection; the branch controller has functions such as human-computer interaction, fault alarm, and calendar display. The entire control system is designed with four automatic light switch modes, and the modes can be arbitrarily switched to achieve multi-mode intelligent control of the LED street light system.

Significance of LED street lights

Regarding the future development of energy saving and emission reduction in street lamps, in recent years, with the continuous expansion of China’s urban construction scale and the continuous improvement of construction levels, as an important part of urban construction, the urban road lighting landscape lighting industry has been in recent years. To develop rapidly. The power consumption of street lighting accounts for 30% of the total power consumption of national lighting. Today, with the increasingly tight energy resources and the persistently tight power supply, the problem of saving electricity for tens of millions of street lights across the country has attracted the attention of government departments. Low-efficiency, high-consumption traditional urban lighting has become an important area for energy conservation and consumption reduction. To this end, the Ministry of Construction and the Development and Reform Commission have clearly proposed that urban road lighting should develop in the direction of “green lighting” that is “efficient, energy-saving, environmentally friendly, and healthy.” As a new darling of the urban lighting industry, LED lamps are a new generation of light sources with environmental protection and energy saving advantages-low frequency induction lamps are used in street lighting, and have been promoted in some cities in China. Low-frequency induction lamp street lights with environmental protection, energy saving and other advantages have great market development potential and huge social benefits. In terms of energy saving, through comparative analysis, a set of 400 watts of conventional street lights (actual power 450W) consumes more than 1970 degrees per year (calculated based on 12 hours / day, 365 days / year), which is equivalent to more than 800 kilograms of standard coal. If a set of 210-watt LED lights is used to replace conventional street lights, it can save 1,050 degrees of electricity a year, saving more than 400 kilograms of standard coal.

In order to further improve the energy-saving effect of LED street lights, people began to use intelligent control technology for timely control to promote the modernization and development of cities.