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LED car headlights / headlights design points
Mar 29, 2018

LED is not unfamiliar to consumers, has been widely used in the car, according to different performance requirements to select the appropriate LED products, LED compared to traditional light sources in addition to the appearance of different, the efficiency of the output and light output is also not large In the same way, when applied to headlamps, the design concept of optical design and heat dissipation will be different from that of traditional lamps. However, because it is different from the characteristics of traditional light sources, when it is successfully integrated with the vehicle body to overcome technical difficulties, it will create a new model for the vehicle. Design concept.

LED on the car

LED has been widely used in the car's related lighting or instruction light source, from Figure 1, we can see from the car dashboard lights, car lights, makeup lights, welcome lights, etc., to the taillights, front and rear lights, Reversing lights, the third brake lights, etc. can be seen related to LED applications.

LED application on the car

From the application history of LEDs, as early as 1992, there were precedents for LEDs to be applied to the third brake lights; in 2000, they were further applied to taillights, turn signals, and brake lights; by the year 2002, Audi A8 took the lead. The LED light source is placed in the front lighting fixture as a daytime running light, which opens up the imagination space for designers and engineers in the front lighting. In the following many international auto shows, LED can be seen as a concept of headlight source.

LED headlight concept car

The LED has advantages of small size in the first place. When used in front lighting fixtures, it can also reduce the size of the entire group of lamps and further allow valuable engine space and other related equipment to be designed with existing halogen bulbs or discharge type bulbs. The total length of the lamps is about 300mm, but in many concept car designs, the LED lamps are only 125mm long. With the advantages of small size, it is also possible to design a variety of different shapes and designs to create different visual perceptions for the body shape. Circular design to escape the traditional lighting fixtures.

Different needs of LED packaging applications

With different application levels, depots also use different LED light sources to meet different environmental requirements. According to different requirements, the brightness can be easily divided into three different requirements for indication, lighting, and projection. The indicator light source can be found on the third brake. Lamps, taillights (taillights, brake lights, turn signals, etc.), sidelights, etc., have low light output lumen values, low power requirements, approximately 70mW to 200mW, and generate less heat to the package, so they are packaged. It will ignore the effect of this heat, and directly use the resin material to cover the entire package. Because of the low thermal conductivity (W/mK) of the resin, the relevant thermal resistance will rise to 50~ 200K/W; while the light source for lighting will have a relatively high package power, besides it can be used for products such as indicating light sources, it can also be used for daytime running light, fog light, front direction light, etc. with higher brightness requirements, but also because The power loss is increased (power is about 1~5W). The heat dissipation part can not consider the heat dissipation problem like the indicator light source. In addition to the resin material package, the metal block is needed to use the heat to maintain the light output efficiency, and the thermal resistance is maintained at 15K/. W below; and cast The light source is the one with the highest brightness requirement for the light source package. Its application product is mainly based on the system (far light, near light, fog light, etc.), and its single package needs to be more than 4W, while the thermal resistance needs to be less than 5K/W. To ensure that the engine room can maintain the cooling capacity at high temperatures, and to maintain the output efficiency of the light source within the available range.

Different application levels, the total brightness requirements will also be different, in the case of internal lighting requires about 80 lumens of brightness, the general choice of surface mount type (SMT) package, single package output of about 2 lumens, the efficiency of up to 15 ~ 20lm/W. For the third brake light, the brightness is about 30lm. Generally, the shell-type package structure (φ=5mm) is used. The brightness of the single package is about 4 lumens and the efficiency is 20~40lm/W.

The taillight group requires brightness of about 300 ~ 500lm, generally use 1W SMT package structure, single package brightness of about 10 ~ 20lm, efficiency of up to 15 ~ 40lm / W. Above are already applied to the body of the light source, and currently The LED factory and the depot are actively cooperating to try to introduce the LED into the front lighting system (headlights, fog lamps). The depot requires about 2,000 lumens of white light for the brightness of the headlamps. The LED factory currently uses high-wattage SMT LEDs. Package structure, the output per package can be 100 ~ 200lm, efficiency is expected to increase to 50 ~ 100lm / W.

The light sources currently used in cars can be divided into incandescent bulbs, halogen bulbs, gas discharge bulbs and LED light sources.

LED headlight design

Before embarking on the design of the headlights, consideration should be given to relevant regulatory requirements, including the requirements for light intensity, environmental testing, and brightness attenuation, and further consideration should be given to related optical design, mechanism design, heat-resistant design, and electrical control design. In terms of optical design considerations, in addition to the reflector design, the LED's own light output type should still be considered. Different types of packages will produce different light outputs, which will further affect the requirements of the reflector or imaging penetration. The traditional headlight design needs to consider different bulbs (H1, H4, H7, H11, etc.) similar. In the traditional headlamp design, the photon of the bulb itself is released from the heated tungsten filament, not due to its own heat or from the engine room. The high temperature affects the brightness output. The heat dissipation focuses on the uniform temperature of the entire headlamp cavity rather than the heat dissipation of the lamp. However, the choice of the headlight material needs to consider whether it can withstand the high temperature from the bulb (headlight cavity is about to bear The temperature of 100°C, the fog lamp cavity temperature can be as high as 300°C), so the materials used here are generally based on heat-resistant materials; however, for LED, the photon release comes from the energy level jump of the PN interface. With temperature Negative correlation, the higher the temperature the weaker light source output, heat dissipation has become an important issue in the design of LED as a light source.

LED problems encountered in headlamp applications

LED is applied to headlights. At various auto shows, various car manufacturers have shown related concept cars. However, in the headlights, there is still no finished product. There are still many problems that need to be solved. The main problem lies in the brightness output, Thermal problems and error design.

The brightness of the headlights requires nearly 900 lumens, nearly 1,100 lumens of light, and an overall demand of 2,000 lumens. It is approximately Lumiled’s production of 40 1W Luxeon emitters with total light output at 25°C, but when its ambient temperature rises to 50°C Its efficiency will be reduced to less than 80%, and its light source output area is about 90_2 (gas discharge type light bulb is about 13_2), and the design difficulty is also increased.

In the LED industry, to deal with the uneven chip caused by epitaxy and the development of the so-called classification of sales process, especially high-wattage chips in the LED industry is the full inspection shipments, according to the classification of the wavelength brightness, and therefore packaged There is a slight gap between individuals, and this gap may exist in brightness, color temperature, or reliability. However, when using LED headlamps, it is inevitable to use multiple chips to output enough brightness for optical design. Special attention must be paid at this time. LED quality testing and quality control to ensure the same quality of light output.

Conclusion

Since declining in 2003, more than 13 depots have exhibited LED headlights at relevant auto shows. For example, the Lexus depot announced that it will launch a mass production of LED headlights in 2007. Car. I believe the relevant engineering problems that exist in the LED will be resolved in the next year of consumers, and let us wait and see.








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