The Trends in Automotive Lighting with LED

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DR. JOHANNES HEIDENHAIN GmbH

ROHM Semiconductor GmbH

KINGBRIGHT ELECTRONIC EUROPE GmbH

OSRAM Opto Semiconductors GmbH

LED technology for automotive has developed strongly in recent years. Among other things, the aim has been to meet the demands of headlight manufacturers for smaller components with a high brightness.

The greater the variety of applications in automotive lighting, the more diversified the portfolios of LED manufacturers has become. Osram Opto Semiconductors has been the market leader for automotive LEDs for many years and has played a leading role in shaping key development trends. Solutions with several thousand light pixels promise completely new possibilities for headlight manufacturers and OEMs – even beyond classic lighting.

Energy Efficiency and Design Freedom in Modern Cars

Automotive lighting has always been an essential safety component – both to see and to be seen. As automobiles have evolved, vehicle lighting has also undergone various stages of change. The faster the cars became, the more important it is to see as far as possible in the dark. In today's cars, factors such as energy efficiency and design freedom are just as important as brightness. LEDs offer a number of advantages over halogen solutions that are still frequently used today. In addition to the purely functional aspects, LED technology is pushing the limits of what is feasible further and further in many respects. For example, manufacturers are increasingly focusing on topics such as communication using light via headlights and rear lights.

Increased Brightness and Better Energy Efficiency

Many of today's vehicle models use conventional lighting technologies such as halogen or xenon. However, the constant technological improvements of LED technology ensure that this balance of power is shifting more and more clearly in the direction of LEDs - and will continue to do so in the coming years. The reasons for this are manifold. With LEDs, the right light wavelength can be easily generated. They require little energy and installation space and have a much longer lifetime than previously used lighting technologies.

With the Oslon Black Flat and Oslon Compact LED series, Osram Opto Semiconductors has launched two product families whose design is trimmed to achieve the best possible ratio of energy efficiency and brightness. The second generation of the Oslon Compact PL has several variants – with one four LED chips. A special electrically insulated pad ensures significantly simplified heat dissipation from the ceramic components.

As a result, the LEDs can be driven at a higher current, resulting in an outstanding brightness value of 395 lumens at 1 A for the 1-chip variant. The dimensions of 1.9 mm x 1.5 mm x 0.73 mm also enable space-saving system designs, which are important for Adaptive Driving Beam systems, for example. Thanks to the once again significantly improved efficiency values within the Oslon Black Flat S family with 130 lm/W at 1 A, the replacement of any halogen solutions previously used is now even more attractive. These improvements also contribute to the fact that the required heat sink can be considerably smaller – with correspondingly positive effects on the overall costs of the system. And, in the future, even LED solutions can be realized without their own heat sink.

More Freedom in Lighting-Design

One of the central arguments for LED-based headlights is the compact dimensions of the diodes. The exceptional light output with extremely small space requirements offers significantly more design freedom than conventional system approaches. This makes the latest trend with LED technology easy to achieve.

The "face" of the latest vehicle generations has changed more and more over the past years. Especially in the premium segment, there is a clear trend towards ever slimmer headlamp designs. This requires not only particularly compact LEDs, but also a high light output. Osram has therefore created the Oslon Boost family. This family is measuring 1.9 mm x 1.5 mm x 0.73 mm, the ceramic-based SMD component is not only extremely small, but also boasts an outstanding luminance of 255 cd/mm². The first LED-based solutions for adaptive front lighting with mechanical dimming were implemented several years ago. This allows individually switchable areas of the high beam to be dimmed or switched off. This prevents oncoming drivers from being dazzled.

Adaptive Front Lighting Demands for Higher Resolution

The combination of high-performance LEDs with intelligent functions will make an additional contribution to significantly improved road safety in the future. Solutions with individually controllable LED pixels are a big step forward. Here, individual, wide segments of the field of view and significantly smaller and more precisely defined areas, such as the windshield of an oncoming car, can be selectively faded out, and at the same time details, such as approaching cyclists on the road, can be illuminated.

A 2D matrix involves elements with less than 0.5° – a significant leap compared to fade-out with LED segments, which are typically about 1 to 2 degrees wide. Active LED pixel arrays are to be highlighted as the best energy-optimized approach for adaptive front lighting systems to date. In current solutions several discrete LEDs, such as Osram's Oslon Compact CM, are used.

Each LED acts as a single "pixel". A special primary optics stretches the upper and lower pixel rows vertically by several degrees. The horizontal resolution can thus be left at about 1.2°. This not only reduces the number of required LEDs, but also allows the use of conventional methods of integrating electronics.

1,024 Led Pixels Can Be Controlled Individually

If a significantly higher number of active pixels is the goal, the integration of the driver electronics and the active LED is already necessary at semiconductor level. This was done in the world's first hybrid LED "Eviyos" from Osram. Eviyos stands for Efficient, Versatile, Intelligent, µ-structured LED chip from Osram Opto Semiconductors. An LED pixel array chip is directly connected to an active silicon IC and controls the individual light pixels. This allows the use of a unit that combines a common power supply with a digital serial interface. Until now, each LED pixel had to be connected to an external power source via two contacts. In the first product generation of the Eviyos, 1,024 pixels are accommodated on approx. 4 mm x 4 mm.

Eviyos technology enables an especially fine LED pixel resolution in the full illumination range without increasing energy consumption. For more frequent distributions without high beam, further energy is saved by switching off the LED pixels. With previous adaptive approaches, the overall solution is always operated at full brightness and unneeded light is manually faded out and thus wasted.

A High Resolution for Automotive Lighting

Around two years after announcing the first hybrid LED, Osram is opening a new chapter in multi-pixel solutions for car headlights with the second generation of Eviyos: more than 25,000 individually controllable pixels can be featured in just 40 mm². The light points move closer together down to a pixel pitch of only 40 µm, enabling particularly space-saving system designs. The second generation of Eviyos is currently still in development and is scheduled to be launched in the year 2023.

With products like Eviyos, applications beyond the classic lighting in cars such as high-resolution projections on the road will also be possible in the future. This form of visualization using light is included in Car-To-X communication. In addition to the projection of information into the driver's field of vision, cars in the future will increasingly communicate with other road users. Thus, rear combination lamps consisting of several LED pixels can function as classic rear lighting in normal operation and, if the situation demands it, only switch on the pixels that form the word "Caution!" to warn the following driver that he is driving too close to the vehicle, for example.

Automotive Lighting Will Change in the Coming Years

A short outlook: The latest advances in development already show how automotive lighting will change in the coming years. The change from halogen to LED-based headlamps will continue to accelerate and penetrate other vehicle classes. Similarly, headlights and taillights will not only illuminate or fade out individual areas with unimagined precision, but also open up new fields of application beyond classic lighting. The new generation of hybrid LEDs heralded by Eviyos enables some additional benefits in car lighting such as lower system costs, and module sizes, lower thermal losses, even higher reliability and better color accuracy. At the same time, the integration of electronics in LED components leads to additional functions.

Osram is clearly showing where the technological journey for vehicle lighting will take us in the coming next years: multifunctional, intelligently controllable headlights that can do much more than just illuminate the road.

* Florian Fink is Marketing Manager for Automotive Exterior at Osram Opto Semiconductors in Regensburg.

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