Audi is the leading brand when it comes to lighting technology for the automotive sector. The company has been the key driver of progress in this area for years, from LED daytime driving lights to the LED headlights available in many model series today. A major design feature, the headlights play a key role in the Audi models’ distinctive appearance. With their good road surface illumination, they also make a substantial contribution to active safety. Technologies such as adaptive light already react to the vehicle’s surroundings and to other traffic participants.
Xenon plus headlights
Xenon headlights are gas discharge lamps. Two tungsten electrodes are sealed in the burner, a thick-walled quartz glass cylinder filled with xenon gas. A concentrated electric arc burns between them. The inert xenon gas filling, which exerts a pressure of as much as 100 bar, gives off a somewhat violet light. Metallic salts in the filling of the gas cylinder reduce its high color temperature to the region of daylight.
Xenon headlights provide a much brighter light and illuminate the road better than halogen incandescent lamps. Including the power required by the ballast, their energy consumption is roughly 20 percent lower. They also last much longer. Audi only uses mercury-free xenon bulbs. Audi is also a pioneer in this field and has introduced this environmentally friendly technology step by step in all its models. Not least due to this initiative, xenon bulbs containing mercury are to be banned throughout the EU from 2012.
Audi offers xenon plus headlights in every model in its line-up, either as standard or as an option. With this technology, a single burner provides both the high and low beam. A switchable shutter is used to change between them. The xenon module is swiveled electromechanically for the adaptive light.
Adaptive light is an Audi technology for the xenon plus headlights and is available in a number of different versions. In the top models A6, A7 Sportback and A8, its controller manages the swiveling xenon plus modules so that they always deliver the perfect light for urban, interurban and highway driving. The driver can set the function of the adaptive light via the Audi drive select driving dynamics system. The all-weather light integrated into the headlight replaces the fog lights.
A particularly attractive element of the adaptive light is the variable headlight range control. A video camera mounted in front of the inside mirror recognizes preceding and approaching vehicles by their lights. In order not to dazzle their drivers, a computer adapts the vehicle’s own light through a smooth range that always provides the maximum possible illumination.
A technological breakthrough from Audi is the networking of the headlight control unit with the optional MMI navigation plus. The navigation system reads the route data in advance and relays them to the light computer, so as to activate the longer-range highway lighting while still on the on-ramp to the highway, for example. The system automatically switches on the cornering lights before entering an intersection; in countries like the United Kingdom, it automatically switches the headlights from driving on the right to driving on the left.
The high-beam assistant, which uses a small camera in the rearview mirror, is available in many Audi models. It detects oncoming vehicles and towns based on their illumination and switches automatically between the high and low beams.
LED daytime running lights and LED rear lights
The daytime running lights of white light-emitting diodes are an Audi feature that underscores the design of the automobiles while simultaneously enhancing safety. Having made their first appearance in 2004 on the luxury Audi A8 W12 sedan, they are now available for every model.
In nearly every case, the LED daytime running lights in a wide variety of designs are integrated into the headlight. The A1, for example, uses a single light-emitting diode per unit. The LED’s light shines into a transparent polymer tube called a light guide to produce a homogenous contour. In the A7 Sportback, the daytime running lights of the optional LED headlights are also linear, but comprise 18 individual LEDs behind a polymer body.
Light-emitting diodes are semiconductors that can convert electrical energy directly into light. They are extremely efficient. The LED daytime running lights from Audi consume just a few watts of power, are extremely long-lasting and practically maintenance-free.
Rear lights using LED technology are available either as standard or as an option for all Audi models. They produce a distinctive light pattern that in many cases also produces three-dimensional effects. Unlike incandescent bulbs, light-emitting diodes reach their full light intensity extremely quickly and without hesitation – if the driver has to brake suddenly, the driver behind gains valuable fractions of a second. At a speed of 100 km/h (62.14 mph), this extends the braking distance available to the driver behind by almost six meters (19.69 ft).
The rear lights of Audi’s A8 flagship are particularly elaborate. Apart from the reversing light, they consist entirely of light-emitting diodes; there are 72 LEDs in each unit. Chip-on-board LEDs, which can be packed tightly together with high precision, are used in many areas. The tail lights, which consume only 9 watts per unit, form a trapezoidal contour that appears as an even, homogenous strip. Its upper segment consists of a light guide; a pebbled, reflective free-form area makes up the lower section.
The five-segment brake light is located inside the trapezoid. When the A8 decelerates sharply, the brake light flashes quickly to warn the traffic behind it, and the hazard warning lights are activated when the sedan comes to a stop.
The LED headlights are an area of technology in which Audi is well ahead of the competition. They were introduced in 2008 on the R8 high-performance sports car; since then the brand with the four rings has repeatedly extended its lead. The LED headlights concentrate Vorsprung durch Technik in a visible and tangible way.
With a color temperature of 5,500 Kelvin, the light from LEDs resembles daylight and is therefore much less tiring for the eyes. The light-emitting diodes are zero-maintenance and designed for the life of the vehicle. They also score points in efficiency with their low power consumption. The low beams, for example, consume only around 40 watts per unit, even less than the already highly efficient xenon plus headlights.
The innovative technology of the LED headlights has led to a radically new design. On the Audi A8, for instance, the low beams comprise ten individual lens modules extending through the headlight in a distinctive arc below the chrome contour known as the wing, on account of its shape. Just below this is another arc of 22 white and 22 yellow LEDs for the daytime running lights and the turn signals. Their thick wall technology makes them appear to the onlooker as homogenous, continuous strips of light.
The main-beam headlights are located above the wing. Their light is generated by two powerful four-chip LEDs and a free-form reflection system; an assistance function switches between the low and main beams. Additional high-output LEDs generate the highway light and the cornering light.
LEDs do not reach especially high temperatures. Red light-emitting diodes withstand about 120 and white ones 150 degrees Celsius – much less than halogen headlights, which generate temperatures of up to 400°C. Audi’s designers therefore make sure that the LEDs transmit their heat in a targeted manner to the headlight glass, in order to keep it free of snow in winter and prevent misting over.
Audi has developed a simulation program that displays the flows of air in three dimensions; by wearing 3D glasses, the engineer can see them on a suitable monitor screen.
LED headlights on the Audi R 18 TDI
Audi regards motorsport as an ideal testing laboratory for its technologies, including vehicle lighting. The Audi R 18 TDI, winner of the 2011 Le Mans 24-hour race, demonstrates the considerable potential of LED technology. Its headlights are extremely bright, light in weight and effectively cooled. They were designed in close cooperation between the specialists from Audi Sport and the series-production development engineers.
The rules for the Le Mans 24-hour race provide the designers with a degree of freedom that would not be permitted on a road car, and Audi has made full use of this. The two LED headlights on the R 18 TDI are rated at more than 100 watts each – about three times more than on a roadgoing passenger car. They throw a bright, uniform conical beam that illuminates the entire road surface and extends more than a kilometre in front of the car. The beam has a power of more than 1,000 lux, which is again five to seven times higher than on a production car.
The racing car’s headlights need no electrical cooling. The airflow as the car is driven enters through an inlet at the bottom and passes through an air duct before emerging at the top of the headlight. Inside, the cooling airflow absorbs heat from the LEDs that is dissipated through small graphite foam cooling elements. These are only one square centimetre in area, but operate at high efficiency. The frame holding the reflector and many components of the headlight housing are made from carbon-fibre reinforced plastic. Each complete headlight weighs only about two kilograms.
The equipment and data specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.