It is known that it is more difficult to drive at twilight or night than in broad day light. The most fatal road injuries occur after dark. Similar to fatigue, alcohol, or traffic density, reduced lighting contributes to the impaired ability of drivers to prevent a collision. The ratio of fatal collisions per 100 collisions is growing in roads without street lighting. This is caused by longer visual reaction times because of poor visibility conditions. It leads to increased stopping distances. Maybe an adaptive front lighting system could reduce fatal road injuries during night time.
Researchers at the Fraunhofer Institute for Reliability and Microintegration IZM in Berlin have collaborated with industry partners in the composite project μAFS to develop an adaptive front lighting system. It could help to reduce car accidents by taking into account the current traffic situation. According to Fraunhofer, their lighting system offers considerably more options for precise light distribution compared with common solutions. Additionally, the high-resolution illumination system with more than 1,000 LED pixels requires less energy.
The oncoming traffic, the course of the road as well as the distance and position in relation to other road users are taken into account with the new adaptive front lighting system
The adaptive front lighting system does not blind other road users and illuminates specific areas in a targeted fashion. „We have been able to solidly connect four LED chips having 256 pixel each with the driver electronics chip. Due to this high resolution, we can control the light distribution to the smallest detail.“ explains Dr. Hermann Oppermann, Group Manager in the Department of Wafer Level System Integration at the IZM.
The new headlight blinds other road users less even with a permanent high beam. The driver can alter the light distribution as desired. The oncoming traffic, the course of the road as well as the distance and position in relation to other road users are taken into account. Only the currently needed pixels are switched on. Only 30 percent of the total available light output are normally needed. This is a decisive reason for its energy efficiency.
A contact between the individual pixels and the driver chip makes it possible to control each point of light independently. As one can imagine, this is a challenging task with a pixel size of only 125 microns. „The connections have to be sturdy, and we need good thermal contact to ensure sufficient cooling of the chip,“ Oppermann explains.
Two concepts are pursued now. In one of them, a gold-tin alloy is applied in a pattern onto the chip. It is a well established technology in the field of optoelectronics. Such fine grid structures with intermediate distances as small as 15 microns, as are required for the LED chip, have not previously been possible, though. A gold nano-sponge plays an important role in the second concept. „This nanoporous gold structure has the advantage that it compresses like a real sponge and can be precisely adapted to the topography of the component,“ says Oppermann. A small unevenness of a few micrometers, which inevitably occurs, can therefore be compensated for easily and quickly.
This is because previous solutions have drawbacks: LED lighting systems are relatively large and expensive: one LED is needed for each point of light. Today, up to 80 individual LEDs are commonly interconnected to form a system. In order to produce a coherent beam of light on the road, though, every LED has to have its own, precisely aligned optics. In another approach, the light source is a laser light or an LCD display with LED lighting, which fades areas of the light distribution according to the situation. Since light is produced and reabsorbed, this solution is not very energy efficient. The same applies to the method of shading certain areas by means of mechanical masks. In the latter system, moreover, only relatively large areas can be selectively illuminated and darkened.
Source: Fraunhofer Institute for Reliability and Microintegration IZM