Automotive Engineer

The need to improve vehicle safety through better advanced driver assistance systems and illumination of the road has brought LED headlamp technology to more vehicles. The ability to gain greater control over the light cone and offer features such as navigation-based adaptive lighting and variable headlight range control has hastened the introduction of the technology to a wider variety of vehicles.

Originally used in only luxury sedans and sportscars, such as the Audi R8 and Lexus LS600h, LEDs are now beginning to filter down to other vehicle segments. OEMs and Tier One suppliers believe that full LED headlights are only 10 years away from being standard fittings in the majority of vehicles. The new Audi A3 will be the first C-segment vehicle to use LED technology in its headlights.

But while LEDs offer greater durability and better light quality than traditional light sources, engineers are working on the next generation of lighting technologies that could offer greater functionality, improving safety further while also mitigating packaging challenges associated even with LEDs and other light sources.

Research is being conducted on organic light emitting diodes (OLEDs), moulded interconnected devices and laser diodes.

OLEDs are the next step in LED technology. The system replaces the semiconductor with organic materials. The organic paste is spread extremely thinly – only a few thousandths of a millimetre thick – on a flat surface, such as highly polished display glass. When an electrical voltage is applied, the molecules in the paste emit photons and the surface lights up. Depending on the distribution of the electrical input, the illumination can be either uniform, include specific light-dark effects or generate dynamic movement.

But due to the inferior quality of the light compared with standard LEDs, it is unlikely that the technology will be used in vehicle headlights.

Tail lights

Steffen Pietzonka, head of lighting at Hella, says: “A normal LED is a point light source in combination with an optical system. It is designed to produce light far down the road. An OLED’s USP is that it is a very thin, very flat homogeneous light source. You need that in the car interior or in the tail lights, but it is not possible to create a huge lumen output.”

But while OLEDs may have limited ability at the front of the vehicle, engineers are using the technology to great effect at the rear. An OLED swarm has been developed by engineers at Audi. The swarm transforms the rear of the vehicle into a large, continuously illuminated surface, using a large number of small points of light.

Movements of the red dots take their orientation from movements of the vehicle. When a right turn is made, they flow to the right; when the car is braked, they flow rapidly forwards.

The faster the car is driven, the faster the dots move. Because of this, following drivers can always see what the driver of the car in front is doing. The OLED swarm combines an attractive visual effect with a specific gain in safety.

OLED technology is not the only system that is being researched by Audi. Its engineers are also developing more versatile lighting systems that can be used for the interior of the vehicle, at the rear and even at the front. Moulded interconnected devices (MIDs) allow engineers to create any shape light assembly, while still allowing it to be illuminated using LEDs. 

MID technology is based on a plastic that contains an organic metal material. The required shape is produced using injection moulding and a laser inscribes the electrical circuit. The uppermost polymer layer is vaporised and the metallised core to which metals can adhere is exposed. Circuit paths are integrated into the moulding, which supplies electric current to the LEDs.