High-brightness light-emitting diodes (hereinafter referred to as HB LEDs ) have been widely used in the fields of indication, display, illumination, etc. as optoelectronic semiconductor devices. It is widely expected in the industry that HB LEDs will be widely used in the field of automotive lighting. At present, in terms of automotive lighting and signal lighting, such as turning lights, license plate lights, brake lights, etc., there are indeed many models that have already applied LED lamps, but the application in the field of headlamps is still rare, only the Audi A8L and so on. A few models are used. The gap between this status quo and the general expectation is due to material cost factors, but the lack of HB LED single module power and high power application thermal management requirements are still the key to the failure to be widely applied. Through in-depth understanding of the performance requirements of modern cars for headlamps, the author discusses some of the above two key issues.
Advantages of headlamps using HB LEDs
LEDs have been in existence since the 1950s and have undergone more than half a century of development. High-brightness white LEDs for lighting have made breakthroughs in the mid-to-late 1990s. The application of expanding HB LEDs has not stopped for more than a decade. HB LEDs are applied to the following features available in the automotive headlamp field:
Long life and superior reliability
The expected life of HB LED is about 50,000 hours, far exceeding the service life of existing tungsten halogen lamps, gas lamps and even xenon lamps. In addition, there is no filament, no cavity, strong structure, and it is not susceptible to bumps and vibrations, which affects normal operation and high reliability. ;
Excellent electro-optic conversion efficiency
Previously (end of 2011) HB LED light efficiency record has reached 230Lm / W, nearly three times the xenon lamp, more than ten times more than tungsten halogen lamp, ordinary inflatable lamp. When the illumination requirement is met, reducing the power consumption can effectively reduce the generator, battery load and wire cross-sectional area, which is conducive to the development of vehicles to lighter weight;
Very short response time
Ordinary light bulbs are hot and inert, and the starting time is about 250mS. The xenon lamp needs to establish the ignition high voltage, and the starting time is longer. LED start-up time is only in the nS level, which in extreme cases can provide more reaction distance for the front and rear cars;
Special requirements for light source for car headlights
The light distribution of the headlights should be such that the low beam has sufficient illumination and no glare, and the high beam has good illumination.
Headlights include far and low beam lights. Both two-lamp and four-lamp vehicles require good convergence and specific distribution of beams. Convergence through lenses and mirrors requires concentration of light sources to facilitate the distribution of light beams. Front lighting is used for light distribution, and illumination and light distribution are equally important.
The headlamps should have good heat dissipation to prevent heat build-up of the light source, and the headlamps can work normally even in a low-temperature freezing environment.
Under the current situation, the headlights of the car are still the most powerful in the conventional lamps of the automobile. The high temperature loss of the lamps will be a dangerous fire hazard. At the same time, the high temperature of the lamps also brings about the impact of work stability and service life. In addition, the thermal accumulation of the luminaire will cause the color temperature of the light source to change, which will cause changes in light penetration performance and reflected light intensity in the rain and fog environment, which will affect driving safety.
Key technical issues that must be addressed by headlamps for HB LEDs
According to the above analysis of the requirements of the headlights and the current status of HB LED technology , the author believes that there are two key problems in the application of HB LEDs in automotive headlamps.
The need to develop small high-power modules is urgent
For the Audi A8LW12, which is the first to apply HB LEDs to the headlights, 76 LED lights are used on each side to meet the illumination requirements. Taking the low beam as an example, the energy consumption on one side reaches 40W. And the complexity of the components, the precision of the combination far exceeds the structure and technical level of the ordinary headlamp assembly.
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