LED car lamp future development trend and application analysis
LED car headlights have finally ushered in the market prospects that are expected to be applied to mass-produced cars after undergoing development stages such as technical verification and concept car display in recent years. There are three landmark events: Toyota ’s Lexus LS600h is the world ’s A listed car with an LED front light source, but it only uses LEDs in the low beam light, and the remote light source is still a halogen lamp. The Audi R8 features full LED headlamps as its main features, while the LEDs used in automotive lighting are provided by Lumileds and Osram. Cadillac EscaladePlaTInum platinum multi-purpose sports car is the first multi-functional sports car with LED headlights.
Unfavorable factors that hinder the rapid development of LED light sources in the automotive market
Does the above-mentioned milestone event mean that LED headlamps will immediately become an innovative technology that dominates the field of automotive light sources? Experts predict: Maybe not. Because even the cost of LEDs can continue to fall at the rate predicted by Moore ’s Law, it will take many years for it to be as low as the HID (High Intensity Discharge) xenon lamp; and the cost of the LED family should be reduced to that of halogen When the lights are comparable, it takes a longer time.
According to Fischer, president of Hella, automotive LEDs currently account for only a small percentage of the light source market, so they target high-volume models (such as the GM / Chevrolet Malibu models). The matching supply is very interested. However, LEDs still have to overcome a series of technical and cost problems to achieve the high level of supply as Malibu models. At least ten years are still needed.
Visteon pointed out that the pace of LED entry into the market is indeed slower than originally expected. We predicted in 2004: LED lights will soon be injected into the market, and HID will be eliminated. Obviously, the current situation is not the same, although it has been expected that LED technology can evolve faster than reality. It seems that high cost is not the only factor hindering the LED market, there are still challenging technical performance issues that need to be overcome.
For example, as far as a single light source is concerned, the light intensity of the LED is still insufficient. The single point is not bright enough to achieve the following wishful thinking: Reducing the number of LED light sources that make up combined lamps will help reduce the space occupied by automotive lamps and facilitate flexible layout, and can simplify the wiring and installation of lighting systems and reduce production costs.
At present, the mainstream status of the LED supply chain is: the LED light source components supplied by Hella to the General Cadillac Escalade models are purchased from Osram; and the Koito LEDs use Nichia ’s light source products and are equipped with Toyota. LS600h model; Philips Lumileds supplies the LED light source to AL (automotive lighting) company, which then configures the Audi R8 with a light system.
According to Koito ’s European and American Operations Managers, they will not self-define the types of light sources and their purchasers, no matter who they are from (Philips, Osram, or Toyota Gosei). Obviously, the first-tier suppliers of lighting system components try to maintain their own flexibility in purchasing light source components and want to observe: which device manufacturer's product technology can make the fastest progress and the most cost-effective.
The photoelectric conversion (light energy density) index of today's LED batch products reaches more than 80 lumens per watt (80lm / W), while HID lamps are 90lm / W and halogen lamps are 201m / W. According to another report from Hella: The index of the latest LED R & D prototype has reached 161lm / W. Hella also predicts that in the next 3-5 years, the LED light intensity from the same power consumption chip will increase by 50%. This not only means that LED lamps will be brighter, but also reflects the reduction in energy consumption, thereby improving the fuel economy of the entire vehicle.
It is estimated that replacing halogen lamps with LEDs can increase the vehicle's mpg (miles per gallon of fuel) indicator by about 0.25. When the European daytime light-on driving regulations are implemented, the mpg increase value can be expanded to 0.5. Lingzhi's model manager pointed out that the application of LED lamps will greatly contribute to the improvement of the vehicle's fuel economy.
However, LEDs with higher light intensity density also emit more heat, and the compact arrangement of the lamp makes the area available for heat dissipation smaller. It is true that low-energy LED devices that belong to the semiconductor category generate much less heat than halogen lamps or HID lamps, but most of the heat of the latter is generated outside the fixtures, while LEDs have low power consumption and little heat. It is necessary to cover the heat in the tiny silicon wafer to conduct.
LED thermal management is a big problem
Even if the small amount of heat is concentrated on the chip-sized device to conduct and dissipate, the small thermal capacity of the device will cause the LED temperature to rise sharply. The operating temperature of the LED must be kept below 150 ° C. One solution to this heat dissipation problem is to use a large number of LED light-emitting elements in a lamp to make the heat generated by a single piece smaller, and then arrange them in a larger space to make it easier to dissipate heat. This is the method used by Koito's headlights when supplying headlights for Toyota's Lexus LS600h.
Each headlight of Cadillac EscaladePlaTInum is composed of 7 LED light tubes, 5 of which are used for short-range beams, and the other 2 are used as remote light sources. They all have their own active cooling devices-cooling fans (similar to the small built-in fans in desktop computers).
According to Hella, thermal management is a design area that makes them particularly bothersome. In terms of program selection, they rely on virtual simulation methods to evaluate and optimize, and the selection of simulation tools (simulation software packages) must pass sufficient experimental data. . He pointed out that the challenge to the thermal management problem not only comes from heat conduction, the heat generated by the LED components can be taken out by means of the "heat pool" device, but also to solve the ventilation problem and let the heat be dissipated from the lamp device. Natural ventilation alone is obviously not enough, so Hella decided to add a built-in fan to the lamp.
Valeo's thermal management strategy is a must. It sets a safe working mode for LED lamps, that is, when the temperature of the lamp rises to a predetermined warning value, it automatically switches to the security mode that reduces the power supply of the lamp by 20%. Allegedly, this level of power supply reduction has little effect on the brightness of the light, but it can significantly suppress the heating level.
LED light source advantages
Since encountering the above-mentioned various cost obstacles and technical difficulties, why do vehicle manufacturers and their lighting system suppliers still insist that Qingshan will not relax and push LEDs into the market?
The reason for this is that this new light source can make the style design and styling arrangement of automobile lamps have unprecedented flexibility and is suitable for the personalization of car models. Moreover, the light output power density of LED can already match that of HID lamps, so it is extremely Hope to eliminate all other existing lighting technologies and dominate the automotive market.
According to Cadillac ’s EscaladePlaTInum ’s model product manager, the LED ’s luminescence spectrum is close to daylight, which makes the light emitted by it reflected by objects (such as road traffic signs / lines) more effective than other light sources, so that it can be farther away. The distance allows drivers to find out early and improve driving safety. He pointed out that almost all road signs use passive glow reflection, because the light color of LED is close to daylight, so that drivers can easily find and see traffic signs at night as well as during the day.
The color temperature of the LED car lamp is 5500-6000K, which is whiter than other light sources, because the light blue color temperature of the HID lamp is 4000K, and the halogen lamp is yellow 3000K. Therefore, in the optical design of HID lamps, the bluest part of the spectrum needs to be moved to the edge of the spot light spot, because these areas are the places where the driver's eyes of the car usually do not pay attention to, thereby reducing the color light to the human eye Discomfort.
However, for the oncoming driver of the meeting, the blue light will cause the other party to dazzle and affect the safety of the car when the vehicle crosses the marginal area. In terms of anti-glare interference, LED headlights have a potential advantage: they can not only protect the comfortable vision of the driver of the car, but also cause visual impairment for the driver of the adjacent car or the meeting car. Because the Toyota Lexus headlights use different light sources (LED / halogen lamps) for the near / remote light, the owner of the LS600h may be disturbed by the poor coloration of different light sources.
Another major advantage for AL (automotive lighting) LED headlamps is that the EU has passed the DRL (daytime running light) regulations that will be effective in 2012, which is in line with Canada ’s recommended regulations (allowing low-beam lights to be used as DRL during the daytime) ) Differently, EU regulations mandate the use of headlamps during the day. As long as the vehicle is in motion, the headlights must be turned on, making the advantages of low energy consumption and long life of the LED light source more obvious.
According to Valeo ’s CEO, another potential that has not yet been realized is: LED headlights can use the array of light spots to combine the active functions of the headlights without using any (currently necessary for such devices) Moving parts. Such an active lighting system (for example, an active security function that changes the direction of light irradiation according to the steering angle) may need to use a larger number of light tubes than previously used to form a lattice. Valeo is proceeding with this idea to develop a new and more reliable new adaptive headlamp system.
Hella Fischer pointed out that this change in the lighting system also conforms to and reflects the general trend that the functions of mechanical devices in contemporary cars are gradually being replaced by (electronic + electronic control + electric) all-electric equipment systems. The same group of LED arrays can be used as the light source of the headlights or the turn signals, but they use their own optical mirror covers when they play different lighting functions.
As a general turn signal, you only need to arrange LED arrays on both sides of the car body, plus a simple switch function. To play the active security role of intelligent front lighting, so that the front light beam can always illuminate the road in front of the vehicle synchronously with the turning trajectory of the vehicle, it is necessary to arrange more light source lattices and take more complicated light spot Control, according to the steering input to control the light and dark combination of the variable light spot array and its mirror, thereby changing the direction of the front beam synchronously.
In short, borrowing from Mr. AsifAnwar of StrategyAnalyTIcs, a market research and consulting organization, although LED headlamps have just started, they will be the fastest-growing areas in the automotive LED market. It is estimated that by 2012, the LED headlamp market will reach 80 million US dollars. With its excellent safety, reliability, energy saving and aesthetic design, LED will become the new favorite of automotive lighting systems, bringing new opportunities for the upgrade and revolution of automotive lights.
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