After undergoing various development stages in recent years, such as technical validation and concept car demonstrations, LED headlights have finally reached a promising stage for mass production applications. Three landmark events mark this progress: the Lexus LS600h from Toyota became the first commercially available vehicle to adopt LED headlights, though only for low beams while retaining halogen lights for high beams. Audi's R8 features full LED headlights, with the LEDs supplied by Lumileds and Osram. Cadillac Escalade Platinum, a multi-functional sports vehicle, is the first SUV to use LED headlights.
Factors hindering the rapid expansion of LED sources in automotive markets:
Do these milestone events mean that LED headlights will immediately become the dominant innovative technology in the automotive lighting field? According to experts' predictions, it may not be so. Even if the cost of LEDs continues to decline at the rate predicted by Moore's Law, it will still take many years for their cost to match that of HID (high-intensity discharge) xenon lamps. For LEDs to reach cost parity with halogen lamps, an even longer period is required.
According to Hella's President Fischer, the current scale of automotive LEDs accounts for only a few percentage points of the light source market, making them highly interested in supplying large-volume models like the Malibu from GM/Chevrolet. However, for LEDs to reach the supply level needed for models like the Malibu, several technical and cost challenges must be overcome, which could take at least a decade.
Visteon pointed out that the pace of LED adoption has been slower than originally expected. In 2004, they predicted that LED headlights would quickly flood the market and replace HID lamps. Clearly, the current situation is not so straightforward. Although there is hope for faster technological advancement of LEDs, high costs are not the only barrier to their entry into the market; there are also technical performance challenges to overcome. For example, the light intensity of individual LEDs remains insufficient. This limitation makes it difficult to reduce the number of LEDs used in combination lamps, which would help minimize space usage, simplify wiring and installation, and reduce production costs.
The mainstream status of the current LED supply chain shows that Hella supplies LED components for the Cadillac Escalade model from General Motors, sourced from Osram; Koito uses Nichia's LEDs in Toyota's LS600h model; Philips Lumileds supplies LEDs to AL (Automotive Lighting), who then configures the headlight system for Audi's R8. According to the manager of Koito's European and American operations department, they do not limit themselves to specific types or suppliers of light sources, whether from Philips, Osram, or Toyota Gosei. It is clear that first-tier suppliers of lighting system components aim to maintain flexibility in sourcing LED components, observing which supplier can achieve the fastest technological progress and the best cost-performance ratio.
Today’s batch-supplied LEDs achieve photoelectric conversion (light energy density) indicators exceeding 80 lumens per watt (80lm/W), compared to 90lm/W for HID lamps and 201m/W for halogen lamps. Hella reported that the latest LED research prototypes have achieved an indicator as high as 161lm/W. Hella also predicts that within the next 3-5 years, the light intensity of LEDs from chips of the same power consumption will increase by 50%. This means not only brighter LED lamps but also reduced energy consumption, thereby improving the fuel economy of vehicles.
It is estimated that replacing halogen lamps with LEDs can improve the mpg (miles per gallon) index of a vehicle by about 0.25. When Europe implements daytime driving regulations, this improvement can expand to 0.5. The model manager of Lexus pointed out that the application of LED lamps will significantly contribute to improving the overall fuel economy of vehicles.
However, higher light density LEDs also generate more heat, while compact lamp arrangements reduce the available cooling area. Although low-power LEDs generate less heat than halogen or HID lamps, most of the latter's heat is generated outside the lamp assembly, whereas LEDs, despite lower power consumption and less heat generation, conduct heat through tiny silicon chips.
Thermal management of LEDs is a significant challenge.
Even smaller amounts of heat concentrated on chip-sized devices can cause temperature spikes due to limited thermal capacity. The operating temperature of LEDs must be kept below 150°C. One solution to this heat dissipation problem is using more LED elements in a lamp, reducing the heat generated by each one, and arranging them over a larger space for better heat dissipation. This is the method adopted by Koito when supplying headlights for Toyota's Lexus LS600h.
Each front light of the Cadillac Escalade Platinum consists of seven LED tubes, five for near-range beams and two for long-range beams. Each has its own active cooling device - a cooling fan (similar to those found in desktop computers).
Hella stated that thermal management is a particularly challenging design area. They rely heavily on virtual simulation tools to evaluate and optimize solutions, ensuring sufficient experimental data verification. They emphasize that thermal management challenges come not only from heat conduction, which can be addressed by "heat pool" devices to extract heat from LED components, but also from ventilation issues, ensuring heat disperses from the lamp assembly. Natural ventilation alone is insufficient, so Hella decided to add internal fans to the lamps.
Valeo's thermal management strategy is unique. They set a safe operating mode for the lamps, automatically switching to a mode that reduces power supply by 20% when the lamp temperature reaches a preset warning value. This reduction minimally affects brightness but significantly suppresses heat generation.
Advantages of LED light sources in automotive applications:
Despite the various cost barriers and technical challenges mentioned above, why do automakers and their lighting system suppliers remain committed to advancing the adoption of LEDs?
The reason lies in the unprecedented flexibility that this new light source offers for designing and styling automotive lamps, suitable for personalized models. Moreover, LED's light output power density can already rival that of HID lamps, making it highly likely to eliminate existing lighting technologies and dominate the automotive lighting market.
According to the product manager of Cadillac Escalade Platinum, the color spectrum of LED emission is close to daylight, making its reflection off objects (such as road signs/lines) more effective than other light sources, allowing drivers to detect them at greater distances and enhancing driving safety. He pointed out that road signs mostly use passive glow reflection, and since LED light colors resemble daylight, they enable drivers to see and recognize traffic signs at night as conveniently as during the day.
LED headlights have a color temperature of 5500-6000K, whiter than other light sources, as HID lamps emit a pale blue light with a color temperature of 4000K and halogen lamps emit yellow light at 3000K. Therefore, optical designs for HID lamps need to push the bluest part of the spectrum to the edges of the beam spot, where the driver's eyes usually do not focus, thus reducing discomfort caused by this color. However, for oncoming drivers, blue light can cause glare when vehicles cross these marginal areas, affecting safe passing. In terms of anti-glare interference, LED headlights have potential advantages: they can protect the comfort vision of the driver of their own car without causing visual obstacles for neighboring or oncoming drivers. Since the Lexus LS600h uses different light sources (LED/halogen) for near and far beams, owners might be troubled by noticeable color differences between the two.
Another major advantage of AL (Automotive Lighting) LED headlights is the DRL (Daytime Running Lights) regulation passed by the EU and coming into effect in 2012. Unlike Canada's recommendation to use low beams as DRLs during the day, the EU regulation mandates the use of headlights during the day. As long as the vehicle is moving, the headlights must be on, making the low energy consumption and long life of LED sources more apparent.
According to Valeo's CEO, another unfulfilled potential is that LED headlights can use point arrays to create active functions without any moving parts currently required. Such active lighting systems (for instance, adjusting light direction according to steering angles for active security), might require more light tubes to form the array. Valeo is developing a more reliable adaptive front-lighting system along this line of thought. Hella Fischer pointed out that this change in lighting systems aligns with the trend of mechanical functions in modern cars being gradually replaced by fully electric systems. The same LED array can serve as the light source for both headlights and turn signals, using different optical lenses for different lighting functions.
As general turn signals, only LED arrays on both sides of the body and simple switch functions are needed. To achieve intelligent active security, allowing the headlight beams to always illuminate the road ahead in sync with the vehicle's turning trajectory, more light point arrays and complex electrical controls are required. Adjustments based on steering input control the brightness combinations of the point arrays and their reflectors, synchronously changing the direction of the headlight beams.
In summary, borrowing the words of Asif Anwar from the market research and consulting firm Strategy Analytics, although LED headlights are just beginning, they represent a rapidly developing field in the automotive LED market. It is projected that by 2012, the LED headlight market will reach $80 million. With its excellent safety, reliability, energy-saving capabilities, and aesthetic design convenience, LED will surely become the new favorite in automotive lighting systems, bringing new opportunities for upgrading and revolutionizing car lights.