Discussion on the design process of intelligent LED lighting system

With the development of LED technology, Internet of Things technology and wireless communication technology, LED lighting particles have gradually developed into commercialization stage due to their advantages of no pollution, long life, good directivity and easy transportation. Due to the unbalanced development of China's LED industry and the lack of LED expertise of some related engineering personnel, the use of LED lighting particles and the irrational phenomenon of LED lighting system design has been caused blindly. Starting from the principle and characteristics of LED lighting particles, combined with engineering practice experience, the design process and precautions of LED lighting system were discussed, and suggestions for solving the corresponding problems were given.

With the gradual emphasis on semiconductor lighting technology in China, the National Semiconductor Lighting Industry Project was officially launched in June 2003. In December 2007, the Ministry of Science and Technology and the State Administration of Foreign Experts jointly approved 33 units to establish a national-level international joint research center, the Chinese Academy of Sciences Semiconductor. It became the “National Joint Research Center for Semiconductor Lighting International”. Until July 2008, the successful completion of the sixth working meeting of the National Semiconductor Lighting Engineering Coordination Leading Group demonstrated the research and application of semiconductor lighting technology for further implementation. The National Medium- and Long-Term Plan for Science and Technology Development is of great significance and also points the way for the development of lighting technology.

On October 12, 2009, the National Development and Reform Commission, the Ministry of Science and Technology, and the Ministry of Industry and Information Technology jointly formulated the “Opinions on the Development of Semiconductor Lighting Energy-Saving Industry” and proposed that “by 2015, the average annual growth rate of semiconductor lighting energy-saving industry output value will be 30%. Left and right, the market share of products has increased year by year, functional lighting has reached about 20%, and the market share of products such as landscape decoration has reached more than 70%. In particular, the application of integrated sensing energy-saving emission reduction control systems such as Internet of Things technology, wireless sensor network technology and smart grid makes the energy-saving intelligent LED lighting control system applied to intelligent buildings, smart appliances and traffic lighting. The 29th Olympic Games in Beijing in 2008 and the Shanghai World Expo in 2010 made a perfect interpretation of the development of the LED industry, as shown in Figure 1 and Figure 2. The number of LED street lamps in China in 2008 is 600,000 盏, and it is expected to grow rapidly to 5 million 2011 in 2011, with a compound annual growth rate of 102.7%. It is estimated that by 2013, China's LED lighting market will be applied to the LED market scale of street lamps. The compound annual growth rate will reach 38.8%, and the annual average compound growth rate of the LED market for landscape lighting will reach 21.7%.

First, the principle and characteristics of LED lighting particles

LEDs, or light-emitting diodes, are solid-state semiconductor devices that convert electricity directly into light. The core structure of the LED is a semiconductor wafer with one end attached to the holder, one end being the negative pole, the other end connected to the positive pole of the power supply, and the entire wafer is encapsulated with epoxy (glue).

Figure 3 LED structure diagram

The LED structure is shown in Figure 3. The basic structure includes: epoxy resin, wafer, gold wire, silver paste and bracket. The role of epoxy resin is to protect the internal structure of the LED. Adding different materials or shaping shapes can change the color, brightness and angle of the LED light-emitting diode. The wafer is the main component of the LED. The semiconductor wafer consists of two parts: one is a P-type semiconductor, in which the hole dominates; the other is an N-type semiconductor, which is mainly electrons here.

When the two semiconductors are connected, a "P - N junction" is formed between them. When a current is applied to the wafer through the wire, the electron is pushed to the P region, and the electron is in the P region. The hole complexes and then emits energy in the form of photons, and the wavelength of the light, that is, the color of the light, is determined by the material that forms the "P-N junction." The gold wire in the LED is used to connect the wafer pad (PAD) to the bracket and enable it to be turned on; the silver paste serves to fix the wafer and conduct electricity; the bracket is formed by plating the material of the bracket.

The advantages of LEDs over traditional light sources such as incandescent lamps and fluorescent lamps are not only reflected in the quality of illumination, but also greatly improved in terms of production, manufacturing and ease of use. Compared with the older generation of luminaires, the characteristics of LEDs are mainly reflected in the following aspects:

1) The LED is encapsulated in epoxy resin, and the package size of the component is generally small. It is not necessary to consider the extraction of the internal air of the lamp and then inject the inert gas. Therefore, it has good performance in vibration and impact resistance for production and transportation. And the installation and other aspects to facilitate.

2) LED light energy concentration is high, directivity is good, concentrated in a small wavelength window, high purity, brightness attenuation is much lower than traditional light sources.

3) The LED device is a solid cold light source. Due to the epoxy resin package, there is no easy-to-loose structure inside the lamp body, and there are no shortcomings such as filament burning, burning and thermal deposition. The general service life is between 50,000 and 100,000 h, even if Frequent switching will not affect the service life.

4) LED does not add “mercury” in the production process, the waste can be recycled, there is no ultraviolet and infrared rays in the spectrum, the heat is low and there is no stroboscopic, no radiation, and it can be safely touched. It is a typical green illumination source.

5) The LED response time is very fast, at the microsecond level.

6) LED can be driven by low-voltage DC power supply, ultra-low power consumption (single-tube power is 0.03 ~ 1 W), and the requirements for the use environment are low.

7) The LED can use the three primary colors of red, green and blue. Under the control of computer technology, the three colors have 256 levels of gray and can be mixed arbitrarily, which can produce 16 777 216 colors, forming a combination of different light colors to achieve richness. Colorful dynamic changes and various images.

Second, LED lighting system design process and precautions

The basic procedures and precautions for LED lighting system design are as follows.

(1) Identify lighting needs in conjunction with the application environment

Since most of the existing lighting fixtures are basically in the category of traditional light sources, it would be a great waste to completely discard them and build a new LED lighting system. Therefore, objectively analyze the optical structure of existing lighting fixtures, combined with the lighting characteristics of LEDs. And the actual application cost is considered whether to replace or improve.

Some conventional light sources adopt an optical illumination structure that is reflected by the inside of the lampshade and then projected onto the road surface. This structure is derived from the fact that the conventional light source is an omnidirectional light source, so that different degrees of optical efficiency are softly reduced inside the lampshade, and the directivity is used. A good LED light source can avoid such problems. The key aspects of reflector design, optical lens design, high-reliability LED power supply design and field lightning protection are included in the lighting demand demonstration program for demonstration.

(2) Analyze system indicators to arrive at design goals

Under the premise of confirming the lighting demand, calculate the overall lighting demand and the power consumption of the supporting equipment (light pole, lamp holder and solar photovoltaic system, etc.), select the driving, control device grade, shell material hardness and flexibility according to the environmental parameters analyzed. And other parameters.

Since China has become the world's second largest power consumer after the United States, it is necessary to consider whether to introduce a solar photovoltaic power supply system for areas with tight electricity consumption. For the installation angle problem of solar panels, a multi-type sensor fusion digital signal tracking algorithm can be adopted. Use latitude to roughly estimate the slope and other methods, as shown in the table below.

Table 1 Solar panel installation inclination latitude comparison table

(3) Determine the type of use with reference to component parameters

In combination with the component parameter indicators, select electronic components that are not lower than the minimum index requirements. Since the LED optical lighting system is a special system that affects the light output of heat, it is necessary to confirm the driving current and junction temperature of the LED. This link requires actual measurement and cannot Totally dependent on the technical manual.

LED lighting test parameters generally include luminous flux (the ability of the light source to produce a visual response per unit time, the unit is lumens); lighting efficiency (in lumens per watt); correlated chromaticity (the most similar to the color with the same brightness stimulus) The temperature of the blackbody radiator, in degrees Kelvin; color rendering index, the color rendering index of the incandescent lamp is defined as 100, which is regarded as the ideal reference source. The standard test system uses 8 standard chroma samples to test the deviation of the 8 standard color samples under the test light source and the same color temperature to measure the color rendering index of the light source. The value Ra20 ~ Ra100 is the highest with Ra100. The larger the average color difference, the lower the Ra value. Light sources below Ra20 are generally not suitable for general use.

Due to the characteristics of the LED itself, it is necessary to effectively control the operating current of the LED while reducing the maximum operating ambient temperature, otherwise the service life of the LED will be shortened.

(4) Calculate the number and combination of LEDs in combination with actual brightness

Calculate the required number of LEDs based on the drive capability of the different drive circuits and the actual lumens of the LEDs. At the same time, it should be noted that the electrical loss of the drive circuit will reduce the overall lighting effect, while converting the input power into heat, and the efficiency of the drive will vary with the load, so the load quantity or connection method of the design solution cannot be arbitrarily changed.

When LED particles are selected, the LEDs have different luminous intensity, driving current, maximum current, and heat generation due to differences in manufacturing processes of various manufacturers, which may easily cause damage to an LED and shorten the life of the entire lighting system. It is recommended to use a dynamic drive circuit to control the LED array, and try to use the same batch of LED particles from the same manufacturer.

When using array LEDs, you need to pay attention to the combination of LEDs. Commonly used are planar array type and sphere array type. Since LEDs are integrated in high-density areas, heat dissipation should be considered.

(5) Compare design options and weigh cost-effectiveness

Since the LED lighting design is a stage of maturity, at least two sets of alternative solutions are proposed at the time of design, and appropriate solutions are selected according to the actual environmental test conditions, and the advantages and disadvantages between the solutions must be complementary.

Lamps used outdoors should be considered to achieve a certain degree of dustproof and waterproof, and in consideration of heat dissipation, it is recommended to use a heat-conducting plate or to design the lamp housing as a mechanical structure similar to a heat sink.

In addition, the optical characteristics of LED outdoor lighting systems directly affect their output power, light distribution curve and spot uniformity. Optical theory calculation, computer simulation and optimization, precision processing of optical components and mold manufacturing are required in the formulation of high-quality applications. The link eventually forms an optical system with better uniformity, no hot spots, glare and light pollution.

Here you need to pay attention to the cost of lighting. The cost of lighting involves not only the initial production cost of the luminaire, but also the cost of energy consumed by the luminaire for normal operation, and the labor cost of replacing the lamp when the lamp is not working properly. The initial cost of incandescent lamps is very low, but they are less efficient at converting electrical energy into light energy and are prone to burnout. When calculating the lighting cost of an LED, it is generally assumed:

When the light output of the LED lamp is reduced to half, the service life of the LED lamp is terminated. Therefore, the life of the typical LED lamp is assumed to be 75,000 h instead of 100,000 h, and the calculation parameter of the lighting cost becomes the cost of production data and energy loss. The sum of the value of funds such as cost, production and maintenance costs, and currency circulation.

(6) Putting into engineering practice and repeatedly demonstrating improvement

In the engineering practice stage, heat dissipation, anti-static and cost issues should be considered for PCB board design. After the internal test of the prototype is used to verify the optical index, high and low temperature index and electrical system index, it will be sent to a third party (such as the National Electric Light Source Quality Supervision and Inspection Center, National Lamp Quality Testing Center, etc.).

(7) Supervise the construction process and regularly maintain the inspection. Pay attention to the installation process of the LED lighting system.

1) Power configuration. Check if the input power is DC or AC, and configure the leakage protection device and overload protection device.

2) Waterproof structure. LED lighting systems used outdoors are particularly concerned with this type of problem.

3) Real-time monitoring. Check the product for damage before installation.

4) Control the number of LEDs. It is not allowed to arbitrarily cascade the number.

5) Drilling of lamps requires careful discussion. Make sure the lamp is waterproof, dustproof and well cooled.

The basic process and precautions for the above LED lighting system design are based on solar photovoltaic LED street lights, but the design flow and considerations can be applied to other LED lighting system designs.

Conclusion

As a new high-efficiency solid-state light source and semiconductor lighting source, LED lighting system has the advantages of no pollution, long life, good directivity and easy transportation. It has been widely used in lighting systems in hospitals, shopping malls, hotels, schools and schools, accompanied by smart grid. The lighting application of the Internet of Things technology and intelligent monitoring and control system demonstrates the vitality and broad application prospects of the LED lighting system.

In the process of design, installation and use, the LED lighting system design process and precautions described in the article will help to improve the LED lighting system design, improve the safety and reliability of the LED lighting system design, and accelerate the LED lighting system. Commercialization process.

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