Prospects for LED headlights to discuss heat dissipation and brightness issues

Automotive light sources occupy a pivotal position in the field of lighting, and their output accounts for about 10% of the total output of the entire lighting source. If you change the lighting of a car to LED , you need to use 400~600 LEDs. In fact, as early as 10 years ago, LED has entered the journey of entering the automotive field. At present, the proportion of LEDs inside and outside the vehicle has exceeded 80%.

Environmentally friendly and durable LED headlights are beginning to show

Car headlights have always been a tough bone for LEDs. Because of the problem of illumination distance and brightness, LEDs are rarely used for headlight illumination. Efficient heat dissipation by using a highly efficient drive

"There is no doubt that most of the car's headlights are still incandescent." Tony Armstrong, director of product marketing for Linear Technology, said frankly, "However, this advantage will now come from high-intensity discharge (HID). The pressure of the lamp and the high-brightness (HB) LED headlights.” HID lamps were first used as headlights in the late 1990s. However, such lamps are very expensive to produce and manufacture, so their use has been limited to high-end cars.

“About 15% of new cars are currently equipped with HID.” estimates by Paul Decloedt, automotive product marketing engineer at ON Semiconductor. However, because the HID light output is too strong, it poses a risk of glare to close cars and pedestrians.

In addition, the HID starts with a high voltage of 35,000 volts, which may interfere with the car's audio and other electrical appliances. According to the owner of the Xenon lamp, the penetration of the Xenon lamp in rain, snow and fog is relatively poor. Paul Decloedt said: "I don't think it's much worse than the halogen."

Therefore, Tony Armstrong is more optimistic about HB LEDs, he believes that HB LEDs will replace HID in the application of headlights. He said: "HB LED headlights will have a very high growth rate in the next 10 years."

The main bottleneck of LED high beam and headlights is thermal management.

It is not difficult to find that LED headlights are mostly found in high-end cars, especially sports cars. Paul Decloedt believes: "The use of LED headlamps can make more changes in vehicle styling." Because LED headlamps are more compact than incandescent lamps and HIDs, the overall design of the car can be more streamlined. Paul Decloedt further pointed out that "compact" is not only the smaller size of the LED lamp itself, but also that the optical components and electronic circuits are correspondingly slimmed down with the use of LEDs.

In addition, LEDs have many other advantages, such as instant turn-on, no preheating, and easier control of brightness. In addition, don't forget the LED killer into the lighting industry - long life. Due to the long service life of the LED, the problem of replacing the headlight "bulb" is eliminated.

The energy saving and environmental protection of the automobile industry is blowing, and the appearance of LEDs just meets the requirements of green and efficient environment. "LED is a green light source, the spectrum is good in monochromaticity, there is no extra infrared, ultraviolet and other spectrum, no harmful substances, mercury, and little radiation." Liu Wei, senior application engineer of Shenzhen Shiqiang Telecommunications Co., Ltd. said that the LED light source has more High lumens, and LED is a solid-state lighting source. Unlike HID lamps, there are no fragile and movable parts such as quartz glass. It has excellent shock resistance and extremely low failure, and is almost maintenance-free.

LED headlight brightness is still controversial

On the Lexus RX450h forum with standard LED headlights, the LED headlights of the RX450h are being discussed. "Even if you hit the bumper on the front of the sound car, the tangential line is a very light blue light type, even my headlights have better recognition of the residual light." A netizen encounters the RX450h's netizens to describe the LED headlights. actual effect. The other RX450h owner replied, "As long as the owner of the RX450h is clear, the LED headlights are super bright and very focused, although the side looks too light. The LEDs are more concentrated than the HID light source, especially the traffic lights stop. According to the front of the car, the underside of the bumper is very bright, and the mountain road is very safe and bright." The owner was originally a BMW B, and has since changed the Lexus.

In order to compare the performance of LED headlights and HID, it is better for those who have found two models with HID and LED headlights to test at 17:30 in the evening. Test results outside the cement wall 20m show that the LED headlights are brighter than the HID, but some LEDs are not as good as the HID headlights.

The light output per unit of electrical energy consumed by LEDs is indeed higher than that of incandescent lamps, but the advantage of the light output of LEDs is less pronounced than for individual LEDs. In order to obtain sufficient brightness, it is necessary to use LED module illumination. “An LED module does not provide enough light for the high beam and low beam functions. Therefore, you need to use multiple LED modules for each of the low beam and high beam functions.” Paul Decloedt points out that since the car headlights are beam applications, Each LED module requires an optical component (lens or mirror). “This is a major reason why LED low beam and high beam prices are still relatively expensive.” In addition, due to the characteristics of LED modular lighting, it is difficult for automotive regulations to define whether LED headlamps with multiple modules are damaged.

LED headlights are tricky to dissipate heat. In addition, after 5 minutes of the above test, the temperature of the LED headlights was very hot. This in turn exposes another drawback of LEDs: heat dissipation. Paul Decloedt said that the main bottleneck for LED high beam and headlights is thermal management. When the LED is heated, not only will the brightness decrease, but more importantly, its service life may be greatly shortened.

Tony Armstrong calculated the power account for the LED headlight system for the car manufacturer. Each headlight system includes five LED lights optimized for all lighting needs, namely low beam, high beam, steering assist light, limp light and turn signal indicator. Standard headlamps typically require 35W to 50W of power. High beam lamps typically require the same or slightly higher power than standard headlamps, while steering assist lamps, running lights and turn signal indicators require less power. . In total, the entire headlamp system may consume more than 200W of electrical power, which can cause a huge thermal power problem. “This has a fatal impact on LED headlights because the output and operating life of LEDs can degrade rapidly with high temperatures,” emphasizes Tony Armstrong.

Cooling is the most direct way. However, Tony Armstrong reminded headlight designers that traditional heat sinks introduce other issues, including the cost of heat sinking materials and the overall weight of the system. "The most effective way to deal with thermal issues is to minimize the heat generated by the LED driver circuit by using a very efficient driver (more than 93% efficiency)." Tony Armstrong believes that less heat can be used after this method is used. A small amount of copper heat sink installed in the printed circuit board of the LED headlight can easily dissipate the generated heat. The Linear Technology LT3755-2 and LT3756-2 provide over 94% efficiency in boost mode, eliminating the need for any external cooling measures.

The commercialization of overseas LED headlights is not long. There are no follow-up actions by local Chinese automakers. Most manufacturers still hold a wait-and-see attitude. Liu Wei said that the price of LED headlights is much higher than HID, and it is not resistant to high temperatures and requires large heat sinks. "Limited by the actual thermal design, LED light decay, electronic control design and other factors, whether the advantages of LED itself can be truly reflected remains to be seen."

HID and LED headlights go hand in hand

Although the process of adopting LED headlights at home and abroad is different, Ansenmei, Linglite, and Shiqiang Telecom agree that the trend of future headlights is mainly HID and LED. "Especially HID has a high cost performance, it should be more common applications, LED will be applied in high-end models." Liu Wei revealed that there are already local manufacturers in the domestic mid-range car to consider the installation of HID lights .

While cost-sensitive cars are likely to continue to use halogen lamps to provide high beam and low beam functions, in terms of mid-range cars, Paul Decloedt believes it will be the world of HIDs and LEDs. The emergence of the 20W HID eliminates the need for automatic dimming and spray washers, making HID's overall cost even more attractive. Paul Decloedt expects the number of new vehicles equipped with HID to double in the next three to four years.

The LED's home field will be used in other headlamps, such as fog lights, steering assist lights, turn indicators, daylighting lights (DRL), and position lights (Position Light). Paul Decloedt expects that these non-high beam/low beam function LED applications will climb rapidly and their adoption rate will exceed HID. "In the next 5 years from now, 30% of vehicles will be equipped with a variety of LED headlamp functions." But in terms of LED high beam and low beam, Paul Decloedt expects its adoption rate to be less than HID.

In fact, anyone who has experience in driving will know that in addition to the brightness of the headlights related to driving safety, the illumination width and brightness of the headlights are equally important. The actual comparison of LED and HID headlights results in 1.5 lanes: 2 lanes, LEDs still need to be improved in terms of breadth. In short, the LED headlight process depends on LEDs to further reduce the price, solve the heat dissipation and improve the secondary optical system.

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