Improving Adaptive Front-Lighting Systems with LED Technology

BY MARK PATRICK, MOUSER ELECTRONICS

■ Figure 1. Advances in LED technology such as Chip-On-Board and ThinGaN allow a single, compact LED module like this Osram OSTAR Headlamp to power a

Adaptive Front-lighting Systems(AFS) have been a recent automotive lighting technology that promises to increase driving safety for passengers and even oncoming traffic. Cars can adjust headlight intensity and angle based on speed or direction of travel to reduce high beam dazzle, improve visibility when turning, and increase general night time visibility. Up till now, AFS have mainly used mechanical means to adjust a beam created by traditional halogen or HID lighting, but recent improvements in LED technology now allow AFS to work using purely solid state technology.

First seen on Audi’s 2014 top of the line A8 model, LED matrix headlights have an array of individually dimmable LEDs. By adjusting the LED lighting pattern, the headlight module is able to create a variety of adaptive lighting effects while minimizing the use of mechanical actuators. With less moving parts, faster activation and dimming capability, these LED based AFS systems are not only more reliable but enable high speed, precise lighting pattern changes not possible with traditional mechanically actuated adaptive lighting.

Improving night-time visibility with adaptive front-lighting systems

Driving at night is dangerous — statistics show that fatal accidents happen three times more often at night than during the day. Improved night-time visibility can make a huge difference, allowing for better awareness of the road and other vehicles as well as earlier detection of hazards.

In recent years, a number of OEMS have introduced Adaptive Front-Lighting Systems to improve night-time visibility and driving safety. These AFS systems adapt the beam shape, intensity or angle to suit the driving situation, with specific features differing depending on the model.

■ Figure 2. Used in the Mercedes CLS Multibeam headlight, the Oslon Compact LED from Osram is an example of an LED designed for AFS systems.

Most of these AFS systems improve turn visibility by using mechanical actuators to swivel the headlight beam towards the inside of a curve when the car is turning, allowing for better visibility and thus earlier detection of obstacles around the bend.

Some of the more sophisticated AFS systems can also adjust the beam shape to suit road conditions. An example of this type of AFS is the Mercedes Intelligent Light System, which uses a rotating drum with various contours and outlines which can adjust the beam formation. As the drum rotates, it changes the projection of the headlight, forming different beam shapes to suit varying road conditions. For instance, a wider beam is used to give better lateral visibility on country roads, while a tighter beam with longer throw would be used on high speed motorways.

AFS lighting represents a huge leap forward in automotive forward lighting, improving night-time visibility across various driving situations. However up until now, the mechanical actuation systems, especially for the more complex beam forming types, mean AFS adds mechanical complexity to the lighting system, raising long term reliability concerns.

In recent years, LED lighting has moved from illuminating automotive interiors to become a key component in exterior lighting. The compact, energy efficient and fast-activating solid state lighting of LEDs has improved almost every aspect of our brake lights, tail lights, and headlights. Could LEDs transform AFS as well?

Improving automotive lighting

LEDs are a natural fit for automotive lighting, with superior service life, vibration resistance, and energy efficiency compared to traditional incandescent bulbs. As brake lights, the faster activation of LEDs helped give rearward cars additional reaction time. As headlights,

LEDs are able to provide a better colour temperature close to daylight, and since they are a surface emitter, much more of the light they generate is usefully projected onto the road, whereas halogen or HID bulbs lose a lot of lighting efficiency by projecting light in all directions including away from the target area.

LEDs have been adopted for interior and signal lighting since the 1990’s, but despite all their benefits, LEDs didn’t get used as headlights until 2008. The first full-LED headlamp appeared on the Audi R8 as an expensive €3,590 Euro option, and the 2008 Lexus LS600H also featured LED headlamps, albeit only for its low-beams. Unlike interior and signal lighting, headlights required high intensity, white light which was hard to achieve at the time.

However, advances in high-brightness LED technology came quick. Improvements in white LED technology have helped move things along and made LED headlamps much more affordable. Today LED headlights are on everything from high end Mercedes models to the Toyota Corolla ZR.

LEDs aren’t just improving automotive lighting, their compact size, quick activation, and precise dimming are enabling the next generation of Advanced Front-lighting Systems.

Adaptive LED front-lighting

The newest generation of adaptive front lighting systems use compact LEDs arranged in an array. Since LEDs are smaller than traditional bulb lighting, turn on and off faster and can be dimmed, they allow for a variety of AFS effects not possible with halogen and HID lighting.

These LED “matrix” style headlight technology debuted in 2014 on Audi’s A8 and have also been adopted by BMW and Mercedes. LED matrix headlights use compact LEDs arranged in a grid pattern. The illumination originally provided by a single halogen or HID bulb is instead spread across multiple LEDs. The greater the number of LEDs, the greater the resolution of the beam and therefore the more precisely it can be adjusted.

Dazzle free high beams

The headline feature of LED-based AFS systems is their ability to produce high beams which don’t dazzle oncoming drivers. Cameras mounted on the windshield detect oncoming vehicles by their headlight pattern. The oncoming vehicle is tracked and the corresponding LEDs on the headlight array are darkened, with the darkened area dynamically adjusting to the oncoming vehicle’s position as it passes by.

The significance of dazzle-free high beam technology can’t be overstated. High beams significantly increase night-time visibility range, but traditional high beams often have to be turned off to not blind oncoming drivers. Dazzle-free high beams let drivers keep their high beams on without threat to other road users, to see deep into the night at all times.

Precision light control

While bright, HID bulbs can’t be dimmed and take time to warm up. Halogen bulbs start up faster but not as fast as LEDs, and dimming them greatly shortens their service life. The ability to quickly activate and deactivate, or dim to a pre-specified level, sets LEDs apart from traditional bulb-based AFS allowing, LED systems to have much more precise lighting control. Modern matrix lighting systems built around an automotive grade high current LED driver like the ON semiconductor NCV78763 can potentially offer over 1000 brightness gradients controllable at the individual LED level.

This level of precision allows LED based AFS to create sophisticated effects such as eliminating back-glare caused by wet roads, fog or traffic signs by detecting the area of glare and dimming the corresponding LEDs.

Curve lighting

LED-based AFS technology also has the ability to adjust the beam to increase visibility around turns. Besides detecting steering wheel direction and vehicle yaw rate, predictive curve lighting can also occur through camera detection or even the GPS navigation system. When a bend in the road is determined, the emphasis of the beam is shifted towards the direction of the curve, increasing visibility while turning and allowing for earlier detection of obstacles.

The solid state advantage

The advantages that AFS systems bring to automotive forward lighting systems is undeniable, both in terms of increasing driver safety at night and providing headline-grabbing technology for OEMs. Until now, most AFS systems have been implemented using mechanical actuators such as rotating drums and mechanical shutters to change beam patterns, but mechanical systems not only have reliability concerns but also physical limitations.

The use of LEDs in Adaptive Forward Lighting Systems provides a clear set of advantages including faster and more precise beam pattern shaping, graduated dimming, and better long term reliability compared to mechanical systems. Just as LEDs have changed the face of automotive lighting, LED based AFS systems will change the way we drive at night

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