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Light Sources
Fifty percent of all drivers feel stressed in poor visibility conditions.[1] The strain eases if the road ahead is well lit; good lighting is the best night vision system. Ever since cars were invented, HELLA has been setting innovation milestones and pursuing a forward-looking approach to lighting products and systems. We focus on enhancing both driving comfort and safety, plus the attractive design of HELLA lighting products lets manufacturers achieve specific vehicle designs and positioning strategies. Find out more about our range of lighting products and individual product segments.
[1] Frost & Sullivan
Halogen
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Halogen light sources have been used for vehicle lights and in both reflection and projection systems for all other major automotive lighting functions since the early 1960s. Halogen bulbs last longer than simple filament bulbs and are more efficient. Each one contains a tungsten filament, like a normal light bulb, but the gas inside the bulb is a special halogen mixture. This mixture combines with tungsten atoms as they evaporate from the glowing filament and redeposits those atoms on the filament rather than on the inside of the bulb itself, ensuring optimum light emission. The temperature of the filament inside a halogen lamp is higher, and so is the amount of light emitted. In addition to halogen reflection systems, headlamps using a bi-halogen projection system are also used in vehicles. These types of lights can produce both high and low beams with just one projection module, mechanically switching back and forth via a shutter. In the higher position, the shutter creates the specific cut-off line for the low beam lights. When it is lowered, the high beam is released.
Xenon
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Xenon headlamps help save lives. If all of the vehicles on German roads were equipped with xenon headlamps, the number of accidents occurring at night would be reduced by an estimated 50%, and traffic fatalities during the same period would decrease by 18%.[1] Despite the striking benefits of xenon headlamps, more than half of all Germans are not adequately informed about this type of head-lamp system, and almost as many cannot name even one of the benefits of xenon headlamps. This stands in stark contrast to the high levels of owner satisfaction with vehicles equipped with this type of system (96%).[2] Xenon headlamps generate light based on the principle of gas discharge. The high voltage required to ignite the xenon gas – 20,000 volts – is generated by an electronic ballast.
In bi-xenon headlamps, the low beam and high beam lights are generated with just one projection module, which is mechanically switched between low and high beams via a shutter in the headlamp. Since the light retains its color and intensity, the human eye perceives the illumination as unchanged. Compared to a halogen low beam, a xenon low beam is characterized by a brighter and more widely illuminated road. The range of the high beam is much greater, and the edges of the road are illuminated more clearly. With xenon headlamps, the automatic or dynamic headlamp leveling systems always ensure correct beam settings depending on the load, the braking process and/or vehicle acceleration. The vehicle load status is measured by inductive or magnetoresistive axle sensors, and headlamps are repositioned using servomotors. With dynamic headlamp leveling, the vehicle speed is processed via the speedometer signal. This means that the lamps can quickly compensate for braking and acceleration processes. The complete xenon system also includes a power wash system that keeps the headlamp cover lens clean so that the xenon light is directed onto the road and drivers of oncoming vehicles do not have to contend with added glare. Dynamic bend lighting was introduced in 2003 to provide drivers with an improved, larger visibility range. In this system, light modules rotate according to the steering angle. The next stage in development of advanced headlamp systems came in 2005, with the introduction of the Adaptive Frontlighting System (AFS). Based on the VarioX module, headlamp light distribution is adapted to the specific situation according to the vehicle’s speed and steering angle. Then, in 2009, a new breakthrough was achieved: For the first time ever, a headlamp system was combined with a camera as a sensor, allowing the combined unit to rely on data collected from the vehicle’s surroundings alongside data from the vehicle itself. When the adaptive cut-off line (aCOL) is generated in this way, the light cone of the vehicle’s headlamps is controlled so that it ends in front of the other vehicles. Today’s state-of-the-art glare-free high beam systems go one step further, automatically masking areas of the road where lighting could annoy other drivers.
LED
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As a groundbreaking innovation in the field of automotive lighting, LED headlamps mark the current high point of the rapid development process traced by LED technology ever since the first LED automotive lighting functions were introduced, in the form of the center high mounted stop lamp, in the early 1990s.
Reasons for this development are the potentials which the LED has. As it delivers not only environmental benefits, it also enhances the driving comfort with its light colour similar to daylight. Furthermore, the light source also offers a great deal of styling potential, and can help manufacturers create a distinctive image for their brands.
Responsible for the light generation in a LED is a semiconductor crystal that emits light when it is electrically stimulated. As in the conventional light sources, the light distribution can also be generated by using reflection or projection systems. The challenge for both systems includes achieving a good thermal management. The LED chip has to be highly effective in dissipating the power lost by the LEDs and discharging it to the system’s surroundings.
Meanwhile, LED headlamps are not only available for premium vehicles. They increasingly enter mid-size models as well. Whereas, the main lighting functions low beam and high beam are realized with LED in the mid-size models, in the upper class models adaptive systems are increasingly come up. Thus far, LED based systems are available with AFS functionality as well as camera based functions, like the glare-free high beam.
Lighting Systems
One of the first light-based assistance systems was the dynamic bend lighting function, which was introduced in 2003. In this system, the light modules rotate according to the steering angle, nearly doubling the range of visibility in a curve.
One advanced development based on dynamic bend lighting is the Adaptive Frontlight System (AFS). This system uses both the steering angle and the vehicle speed as parameters for illuminating the road. Based on this internal information, a cylinder in the VarioX module is used to create various types of light distribution, including town light, country light, adverse weather and motorway light.
The development of the adaptive cut-off line (aCOL) goes one step further. This feature also utilizes data gathered from the vehicle’s surroundings to generate the light distribution. A camera detects oncoming traffic and cars ahead, and a stepper motor turns the cylinder of the VarioX module to the required position within milliseconds. This means that the light cone always ends directly in front of oncoming traffic, or just behind the car ahead of you.
The glare-free high beam function means that drivers can drive with the high beam on at all times. If the camera detects other traffic on the road, the distribution of light from the high beams is adjusted to mask the specific area.
Now used to illuminate broader areas than ever before, LEDs will also perform the opposite function in the future. Targeted spotlighting functions will allow specific illumination of certain types of objects, such as children playing at the edge of the road. This draws the driver’s attention to these potential risks ahead of time, enabling faster responses.
Adaptive Frontlighting System (AFS)
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The low beam is only a compromise of all partial light distributions. That’s why the dynamic Adaptive Front lighting System was developed to permit the best possible illumination of the road depending on speed and steering angle. Achieving this requires a VarioX projection module with a rotating cylinder between the light source and the lens. Typically, the cylinder has varying contours and can also rotate around its own longitudinal axis. A stepper motor turns the cylinder to the required position within milliseconds.
- Town light, which is activated at speeds below 55 km/h, features a horizontal cut-off line to minimize glare for other people on the road. Wide light distribution also makes it easier to detect pedestrians at the side of the road.
- Country road light is also activated between speeds of 55 and 100 km/h and is similar to conventional low beam light distribution. The VarioX module generates an asymmetrical light distribution pattern to minimize glare for oncoming drivers. The cut-off line is raised so that the left edge of the road is better illuminated, providing greater coverage.
- Motorway light is activated at speeds above 100 km/h. The light distribution range is designed for wide curve radii at high speeds.
- The high beam of the AFS works like a conventional high beam, but does not require the driver to take action to avoid exposing oncoming drivers to excessive glare.
- The Adaptive Frontlighting System also has a dynamic bend lighting function. Depending on the steering angle, the headlamps also swivel by up to 15° and allow optimized illumination of the bend.
- Adverse weather light creates a wider dispersion of the light to improve visibility in rain, fog or snow. This feature also reduces long-range illumination to minimize reflective glare affecting the driver’s own vehicle.
Adaptive Cut-Off Line
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One advanced version of the AFS system with static light distribution is the combination of this system with a camera and image processing functions.
The first step in this direction is the adaptive cut-off line (aCOL):
A camera on the front windshield detects oncoming vehicles and vehicles traveling ahead, and the system adjusts the headlamps so that the light cone ends before it reaches the other vehicles. This allows the range of the low beam lights to be increased from about 65 to up to 200 meters (3-lux line). If there is no traffic ahead, the system switches to high beam, giving the driver optimum visibility at all times. The system also uses vertical angle information to make deductions about road topography, improving illumination in hilly terrain. The possible range of the headlamps is based on a feature that checks the level of glare from other road users. This helps prevent annoying glare and provides maximum low beam light distribution.
Vertical Cut-Off Line
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The objective of the high beam function is to give the driver the best possible visibility while at the same time avoiding exposing other road users to excessive glare. This often proves insufficient, particularly at high speeds and on winding roads. Many drivers, however, choose not to use their high beams because they are worried about exposing oncoming drivers to glare if they do not switch quickly enough to low beams.
Glare-free high beams permit drivers to keep their high beams on at all times, but minimize glare that might annoy other drivers.
This type of system features a front camera, high-performance software and intelligent lighting technology, and automatically masks high beam distribution to areas of the road where it might annoy other drivers. This significantly increases high beam use at night.
If the camera detects road users who are at risk of glare, the area around the road user detected by the camera is automatically masked. This masked sector can even follow that road user dynamically. The area directly in front of the vehicle is illuminated at all times with a standard light distribution pattern comparable to today’s low beam light levels. The brightness of the variable zone above the cut-off line can be adjusted locally. One possible way to provide glare-free high beam functionality is by installing a special sheath on the rotating cylinder in the VarioX® projection module. Based on image processing functions and intelligent settings in the VarioX module, critical areas of oncoming traffic that might face glare are simply removed from the high beam distribution, but the rest of the high beam field remains intact for the driver’s convenience, yielding a considerably greater range of visibility as compared with standard systems.
LED Matrix Beam
The heart of the Matrix LED headlights is the mechanic free glare-free high beam. This allows the driver to travel in his vehicle with a permanent high beam without risk of dazzling oncoming traffic or any preceding vehicles. By means of a camera, oncoming and preceding traffic are detected and then, by the shutting down or dimming of individual LEDs, these vehicles are blanked out of the field of high beam light distribution in real time. The implementation of Matrix technology allows, for the first time, several tunnels to open simultaneously. One example of this is the scenario where several oncoming vehicles are driving one behind the other. While these are “masked out”, the high beam continues to illuminate all the areas between the vehicles and to the right and left of them at full power. As soon as no vehicle is any longer in the driver’s field of vision, the system once again reverts to full high beam lighting. In addition to the specific masking out of other vehicles, the light cone of the Matrix high beam also adapts to the driving situation, for instance in the case of negotiating bends when the dynamic bending light function is required. In such a situation, the intensity of the light cone can be varied on the sides or it can be focused on the middle of the road. Consequently the driver’s visibility at night improves dramatically while, at the same time, the risk of dazzling oncoming traffic is eliminated.
Such a function is technically possible thanks to the splitting up of the high beam into five reflectors, each one having a chip containing 5 LEDs. For the first time ever, the lighting expert, HELLA, has now succeeded in operating every LED on the 5-segment chip separately, whereby a total of 25 LEDs per headlight can be operated on full power or lowered as and when required.
