Light-emitting diode (LED) in automotive lighting applications (Figure)

0. With the development of the automotive industry, automotive lamps (if there is no special description, the car lamps in this article refer to the lights and light signals outside the car) are undergoing rapid changes. Today, LED is the latest generation. The automotive light source is favored for its many advantages that traditional light sources cannot match.

The basic principle of LED (light-emitting diode) is made of semiconductor material, the core of which is PN junction, which has the characteristics of general PN junction, namely forward conduction, reverse cutoff, breakdown characteristics, in addition, Under certain conditions, it also has luminescent properties. It does not heat the filament to heat up like a traditional filament bulb, but instead converts it directly into light, so it is a cold light source.

The peak wavelength X of the light emitted by the LED is related to the forbidden band of the semiconductor material in the light-emitting region. 1240/(ran), the unit of five g is electron volt (eV). If you want to generate visible light (wavelength is 380nm 6~780nm red light), the five g of semiconducting yt should be in three.

Advantages of LED In recent years, LED automotive lamps have become more and more popular. Why LEDs will gradually replace traditional light sources such as incandescent lamps and tungsten halogen lamps. This is completely determined by the characteristics of LED itself. As a kind of cold light source, LED has many The advantages that traditional light sources cannot match. The main ones are: high luminous efficiency, low power consumption; long life, no need to replace during the service life of the vehicle; safe and environmentally friendly, no glass casing for resin packaging, good shock resistance; high light utilization, narrow spectrum, good monochromaticity, no Need a red or amber filter shade; fast response, flexible application and so on.

Of course, from the perspective of social development, energy conservation and environmental protection and versatility are the most important reasons for us to consider the use of LED light sources. If all the external lamps of a regular car are equipped with traditional incandescent lamps and tungsten halogen lamps, the overall power is about 600 W. If all LED lights are used, the overall power is only 60~100W, which shows the energy saving potential of LED light sources. Quite huge. Although the manufacturing cost of LED automotive lamps is relatively high, the use of LEDs is an inevitable result of advances in automotive lighting technology in terms of cumulative energy savings and product quality.

LED car luminaires have been designed from the early red and green light to the development of blue LEDs. By integrating red, blue and green, or by mixing blue phosphors with yellow phosphors, white LEDs have been produced and white light has been successfully developed. LEDs are the biggest benefit to the automotive industry and can be applied to more luminaires such as headlamps, making the application field broad and far-reaching. Advances in technology have greatly improved the luminous flux of a single LED, and at the same time produced a variety of LEDs with different illumination angles depending on the application. Although theoretically, the luminous efficacy of LEDs can be as high as 200 lm/W or more, but the white LEDs produced in China. It is only 63lm/W (110lm/W internationally), and there is still a certain gap with the theoretical value, and its price has certain disadvantages compared with the traditional light source. Therefore, how to bring out the advantages of LED as soon as possible will become our face. Technical problems.

First of all, we must try to improve the quality of the LED itself. The LED package should minimize the total reflection of the light inside the substrate, increase the reflectivity of the substrate, so that as much light as possible can be transmitted to increase the luminous efficacy of the LED. The heat dissipation fp problem is an important factor affecting the LED. The temperature rise will accelerate the light attenuation of the LED, and the temperature at the chip node directly affects the life of the LED. The heat dissipation capability and the temperature of the use environment limit its power. The size of these is a must for designing high quality LED automotive luminaires.

Secondly, after selecting the high-quality LED light source, we can design various types of automotive lamps according to the overall shape of the car. In order to form a good light intensity distribution, each LED light source should be equipped with a light cup, and in order to meet Each LED can be designed to have a different direction of illumination.

Conventional light source automotive lamps generally only contain one light bulb, while LED automotive lamps usually have many LEDs, which are quite different in design. Ordinary light sources usually require a relatively large space for the lamps, while LED lamps can be designed to be flat. (See and show) Because the power of a single LED is extremely low, the luminous flux is small and the angle of its illumination is small, in the design of LED lamps, several, ten or even dozens of LEDs are generally arranged, and the LED illumination angle is The choice is very important, and the reasonable illumination angle can ensure that the number of LEDs is minimized to reduce the cost if the light distribution performance of the luminaire meets the requirements.

And is the comparison of the lighting effect of incandescent lamps and LED lamps.

As can be seen from the sum, the appearance of the incandescent lamp is different, the place near the light source is very bright, the farther away from the light source is darker; the brightness of the LED lamp is very uniform, and the design is very flexible, can form the desired The various graphics, the visual effects are very good.

The working time of the brake light of the automobile is generally short, and the starting speed is required to be fast, and the LED light source has the characteristics of rapid response, so the earliest adopting the LED light source on the automobile lamp is the high position brake lamp.

Nowadays, many car brake lights, position lights, turn signal lights, rear fog lights, reversing lights and other lamps have LED light sources. Through the statistics of the sample inspection data, the quality of these LED automotive lamps has been higher than that of similar incandescent lamps.

Under normal circumstances, automotive brake lights, turn signals, rear fog lights, reversing lights and other lamps such as the use of incandescent bulbs, the power is 16 ~ 27W, if the choice of LED light source, only 1.5 ~ 5W; position lights, position lights, etc. If the lamp is equipped with an incandescent bulb, its power is 5~10W, and the LED light source is generally 0.2~1.5 W, and the LED power will be lower as the technology progresses.

LED car luminaire drive circuit has ordinary battery direct drive, this method often uses voltage divider resistor; also uses PWM drive electric controller to convert the DC voltage on the car into a square wave signal, by changing the square wave duty cycle method To adjust the luminous intensity level of the luminaire, the control is very flexible. The PWM drive circuit is especially useful for lamps that require more than two levels of illumination intensity, such as two light intensity brake lights, rear turn signals, and brake lights/post position lights. In order not to make people feel flickering, the square wave frequency output by the PWM driver circuit should be above 100Hz, and it is necessary to consider the problem of radio frequency interference when designing the PWM driver circuit.

Inspection of 4LED automotive lamps At present, the inspection basis of LED automotive lamps is based on the national standard and ECE standard of each lamp. The test content is mainly the light distribution performance and light color and chromaticity characteristics, and there is no requirement for photoelectric parameters.

4.1 Light distribution performance test In the automotive lamp, the LED light source has two connection modes: series and parallel. When the series mode is used, it is detected as a single light source, and in parallel, it is detected by a multi-source light.

The traditional illuminance meter can accurately measure the light distribution performance of LED car luminaires, while the PWM-controlled LED luminaires use the traditional illuminance meter to detect large deviations, which need to be tested with a dedicated PWM illuminometer. Because the light emitted by the LED has the characteristics of easy attenuation, in the light distribution performance test of the LED lamp, the standard stipulates that the measurement should be performed for 1 min and 30 min. When the luminaire is installed on the light distribution turret according to the reference axis, the test voltage is used ( 13 V) Light the lamp, measure the luminous intensity of all HV points 7imiHv after 1min, and measure the luminous intensity of all test points after 30min. The fc intensity of HV point is 30mtaHV at 30min, the calculation system is 1X=/lminHv//30minHV Multiply the x-intensity value of all the test points except the HV point at 30 millimeters to obtain the luminous intensity values ​​of all the test points except for the HV point at 1 min. The light distribution performance of the lamp can only be judged if the luminous intensity of all test points meets the standard requirements at 1 min and 30 min. According to the standard requirements, if the luminaire is a parallel multi-source, it should also be tested when any light source fails, the light distribution performance should still meet the minimum luminous intensity requirement. In this case, the luminous intensity of all test points should still be measured at 1 min, and The results of each test point must meet the standard limit requirements.

4.2 Light color and chromaticity characteristics test The light color and chromaticity characteristics of LED lamps shall comply with the relevant requirements for the light color and chromaticity characteristics of each functional luminaire in the installation regulations of GB4785-2007 automotive and trailer external lighting and optical signal devices.

The spectral characteristics of the LED luminaire, the chromaticity coordinates, the correlated color temperature, and the dominant wavelength are measured using a spectral analysis system. The spectral measurements of a certain two samples are as shown in the sum.

The spectrum of the spectrum of the red LED light source of I winter 15LED light source is 620~780nm, the chromaticity characteristic is 0.335 and the width is 0.980-X. It can be seen from the test results that the chromaticity coordinates of the two samples are in line with the requirements of red light. However, the LED lamp samples have a peak wavelength of 659 nm, a narrow spectrum, and all in the red spectrum.

The measured incandescent lamp plus red filter sample has a peak wavelength of 780 nm, which is adjacent to the red and infrared light, and contains a small amount of orange light. Since the spectrum analysis system used only scans the visible light region, the true peak wavelength of the sample is very high. It is possible that in the infrared wavelength, most of the energy is wasted by infrared radiation.

5LED car headlights In China's current standard system, only car filaments and gas discharge sources can be used. The latest ECE revision adds the content of the LED light source module. In the ECER112, a new addition of Annex10 is specifically for the test requirements of LED headlamps, which provides a regulatory basis for LEDs used in headlamps.

Since the headlights of automobiles require extremely high brightness, to meet the requirements of the light distribution performance of the headlights, the total luminous flux of the light source should reach 1000 lm or more. Since the temperature rises, the luminous efficiency of the LEDs will decrease sharply, so at the time of design. The heat dissipation of the light source cannot be ignored, and manufacturers have built-in small fans to solve this problem. In addition, the headlights are different from other products, and its quality directly affects the safety of the passengers. When considering the requirements of luminous efficiency and brightness, it is necessary to pay special attention to the quality detection of the LEDs used. Compared with other traditional light sources, Also consider the color rendering and the 1min compliance note after lighting to ensure that its work is stable and reliable. Recently, some high-end models of foreign bungee jumping have been equipped with LED headlamps, which indicates that LEDs have officially entered the automotive headlamp application market.

Recently, there is another good news for automotive LED headlamps: the EU has passed regulations that will take effect in 2012, and it is mandatory to use headlamps during the day, so that the advantages of low energy consumption and long life of LED light sources are more obvious. . Although the cost of LED headlamps is quite expensive, its development prospects are very promising. As long as the attenuation and heat dissipation of the light source are controlled, with the improvement of technology, it is believed that it will become more and more popular in the future.

It is not advisable to use a floodlight to brighten the glass curtain wall.

For example, Helen Hotel, such as hotels and restaurants, has a comfortable and comfortable atmosphere due to the interior of most of its windows. The average illuminance inside the room is 100lx or lower, which is not conducive to outward scattering of light. illumination.

At present, the hotel does not carry out any decorative lighting at night except for the “Helen Hotel” and several back-illuminated characters. The Helen Hotel is located at the junction of Fujian Middle Road and Nanjing East Road, and the west side is Century Square. This special location allows the building to illuminate as a bright spot for more brilliance.

The main body of the building adopts LED outlines, etc. It is not suitable to use fancy patterns. The brightness should not be too high. The lower part of the building should be combined with the inner light. LED decoration can be used in part, and the dynamic light source can set the atmosphere.

The overall illumination of large areas such as light should not be used as shown.

It is advisable to use the internal penetration method.

It is not advisable to improve and expand the urban space function of Zheng Zhengling, Qi Huifeng and Wang Weiqiang. Urban Planning Journal, edited by Wu Mengyou and Yin Yanming in 2000. Urban commercial street lighting environment design. China Building Industry Press, 2006 4 Nanjing Road Pedestrian Street overall renovation planning and design guidelines - architectural night lighting design guidelines GB500342004, architectural lighting design specifications DB31/T3162004, urban environment (decorative) lighting specifications 7 old Landscapedesign magazine editor, Zhang Qi, Liu Yunjun translated. World Urban Landscape Lighting, Dalian University of Technology Press, Liaoning Science and Technology Press, (Continued from page 7) 6 Conclusion LED automotive lamps with their huge energy saving potential, safe and environmentally friendly quality, flexible design and good lighting Quality has opened up a whole new field of technology for us. Despite the high production costs, the use of LED automotive lamps in new models introduced in recent years has become very popular, and some high-end models have also introduced LED headlamps. With the advancement of technology, it is believed that in the near future, automotive lamps will all adopt LED light sources. LED, a technology that illuminates the future, will surely lead the automotive industry to a more awkward future.