Analysis of key technologies of LED-based automotive rear combination lights

　　1 Introduction.

　　With the rapid economic development in recent years, the design and manufacturing technology of automobiles are also improving day by day, and the functions of automobiles are gradually enriched. Automobiles have become an indispensable part of people's daily life. However, the possibility of traffic accidents when driving at night or in low light conditions is very high, accounting for about 27% of the total traffic accidents, and most of the time there will be personal injury. Therefore, good lighting facilities are necessary for driving at night.

　　2. The development of automotive lighting .

　　The development of automobile lighting began in the 1880s. The first automobile lighting fixture in the world was a hanging gas lamp for a classic car. The first electric lighting fixture was developed in 1912. In the early days, automobile lighting was incandescent lamps, which were dim. With the increasing number of vehicles and the increasing speed, incandescent lamps could no longer meet the daily lighting needs. Therefore, automobile lighting has developed into a series of lamps with higher brightness, such as halogen tungsten lamps, high-intensity gas discharge lamps, brake lights, turn signals, and rear fog lights, which play a key role in avoiding rear-end collisions or collisions when turning at night. With the improvement of productivity, lighting technology is also gradually developing, including the application of light emitting diode technology (LED) in automobile lighting, especially in automobile lighting. In recent years, the use of LED headlights has become more and more common in automobile design, and the shape has become more and more beautiful. The combined use of various lamps has led the trend and direction of the development of automobile lighting today.

　　3 Basic theory of automobile rear combination lamps.

　　When driving, the rear combination lights can clearly indicate the driving, parking and turning status of the car, allowing drivers of various vehicles to make more reliable adjustments and drive safely. Nowadays, the rear lights of cars generally adopt the form of combination lights that install signal lights of various functions in the same lamp body, which is beautiful and easy for car drivers to identify. Nowadays, general rear combination lights include brake lights, rear fog lights, turn signals, reversing lights, rear position lights, etc. These lights have their own functions, as follows:

　　Brake lights: General brake lights are installed on both sides of the rear of the car. When the driver steps on the brake pedal, the brake lights will light up and emit red light to remind the vehicles behind to pay attention and not to rear-end. When the driver releases the brake pedal, the brake lights will go out.

　　Rear fog light: A rear fog light for a vehicle is installed at the rear of the vehicle to make it easier for other road traffic participants behind the vehicle to be spotted in low visibility environments such as fog, snow, rain or dust. Its luminous intensity is greater than that of the taillight.

　　Turn signal: The turn signal is an important indicator light that is turned on when a motor vehicle is turning to alert vehicles in front, behind, left, and right, as well as pedestrians.

　　Reversing light: A white light that illuminates the road behind the vehicle and warns other road users that the vehicle is reversing or about to reverse.

　　Rear position lights: commonly known as small lights, they are mainly used to indicate the presence and approximate width of the car, making it easier for other vehicles to make judgments when meeting or overtaking.

　　4 Design technology of automobile rear lights.

　　The design of LED rear combination lamps includes thermal, mechanical, optical and circuit design calculations, and these four aspects are inseparable. Design technicians must make comprehensive considerations and combine the streamlined aesthetic requirements of advanced automobile design to design a practical, durable and beautiful rear combination LED lamp.

　　The design of rear combination lamps for automobiles should first determine the number of LED lamps. For floodlighting systems, the VH system is generally used for analysis; for general estimation of the total minimum luminous flux of signal lamps, the spherical zone coefficient method is more commonly used, that is, the method of block calculation and accumulation. The most important thing is optical design. At present, optical design mainly adopts light distribution test. Abandoning the traditional empirical design, optical design software is generally used to perform computer-aided simulation of automotive LED rear combination lamps. Using computers to intuitively perform optical tests on lamps, the results are relatively intuitive and accurate, and the adjustment is convenient, which reduces unnecessary waste of manpower and material resources, improves R&D efficiency, and optimizes research ideas.

Figure 1 Optical analysis flow chart

　　The basic steps of optical analysis in TRACEPRO are as follows:

　　There are two ways to build an optical model: one is to build a model based on the geometric structure of the LED; the other is to build an optical model based on the characteristics of the material surface. The difference between the results of building an optical model based on the surface characteristics of the material and the measured value is within 5%, which is closer to the measured value. In addition, the modeling is easy, the data is reliable, the model is simple, and it has promotion value.

　　Heat dissipation design is a crucial part of LED lamp design. Whether the heat dissipation is good or not determines whether the service life of the lamp can reach the set value. When electrical energy is converted into light energy, there is energy loss, and part of it is converted into heat energy. Such heat seriously affects the luminous flux, main wavelength, circuit failure and even the failure of LED lamps, so attention should be paid to the improvement of heat dissipation measures. We can consider the following aspects: improve the thermal conductivity of the bracket material and increase the contact surface with the air; optimize the design of the circuit board, pay attention to the position of the circuit cathode heat dissipation and the current limiting resistor; pay attention to the position between various combination lamps to expand the heat conduction efficiency; choose suitable reflectors, light distribution mirrors, and lamp shell materials to improve the overall heat resistance of the lamp body.

　　5 Conclusion.

　　The design of LED rear combination lamps includes thermal, mechanical, optical and circuit design. The most important of these is optical design. Currently, computer simulation is used for optimization design. There are two main methods: one is to establish a model based on the LED geometric structure; the other is to establish an optical model based on the characteristics of the material surface. The second method is reliable and has promotion value.

　　Heat dissipation is a difficult problem to solve in the design of combined LED lamps. Whether it can be handled well is the key to the success or failure of LED designs. How to improve heat dissipation efficiency requires further research.