Car lights: Without me, no matter how good the car is, it’s useless

If we were to select the most important means of transportation in modern human society, cars would undoubtedly top the list. As an indispensable and loyal companion for people to travel, the importance of cars is self-evident.

It has greatly broadened people's activity radius, improved life and work efficiency, and made it possible for people to exchange a shorter time for a larger space. "Leave in the morning to the Green Mountains and arrive in the evening to the Bright Moon" is no longer out of reach. For this reason, the development of automobiles is closely related to the progress of the entire human race, and the history of automobile development is also the history of human technological progress.

Image source: veer gallery

Since the German Karl Benz (Mercedes-Benz is named after him) invented the car in 1885, car lights have also been born as an auxiliary tool on the car. As the eyes of the car, the headlights have always been an important "organ" to ensure the normal and safe operation of the car.

The world's first car, Mercedes-Benz No. 1. Image source: Photographed by the author

Designing car lights that are refreshing and unique has become the finishing touch that car engineers are constantly pursuing. Some car lights are colorful and "send a glance"; some car lights are sonorous and powerful, like a battle axe. The unique car lights have even become a major selling point for some luxury cars and have gradually become their own business cards.

Some distinctive headlights, Image source: Made by the author

Starting from the initial portable kerosene lamp, the development of automobile lights has roughly gone through four stages, namely the first generation of incandescent lamps, the second generation of halogen lamps, the third generation of high-pressure gas discharge lamps, and today's latest fourth generation LED (light-emitting diode) lamps.

Part 1

Ancient incandescent lamp

The incandescent lamp invented by Edison in 1879 was destined to become the first choice for car lights to replace the original portable kerosene lamps, especially in some classic cars. Incandescent lamps still have a place in the current lighting market. It is a tungsten filament that heats up to incandescent state by passing current through it. The temperature can reach 3000℃. The high-temperature tungsten filament emits photons for lighting.

However, when the tungsten filament is working at high temperature, it will continuously volatilize tungsten atoms and eventually cool on the inner wall of the glass tube, which makes the life of the incandescent lamp very short. In order to avoid the rapid loss of the tungsten filament, its operating temperature has to be lowered, which in turn limits its brightness. Due to the lower color temperature, the incandescent lamp emits a yellowish color. Fortunately, the limitations of incandescent lamps as car lights were soon made up by halogen lamps.

Image source: veer gallery

Part 2

Advanced version of halogen lamp

Halogen lamps began in the 1970s. They are actually an upgraded version of the above-mentioned incandescent lamps. By adding halogen elements (iodine or bromine, etc.) to incandescent lamps, the brightness of incandescent lamps can be increased by 1.5 times, and the service life can be increased by 3-4 times. Its working principle is: when the tungsten atoms produced by the filament at high temperature are evaporated and move toward the glass tube wall, when approaching the glass tube wall, the tungsten vapor is cooled to about 800℃ and combines with the halogen atoms to form tungsten halide (tungsten iodide or tungsten bromide). The tungsten halide turns back to the center of the glass tube and continues to move, and then returns to the oxidized filament.

Since tungsten halide is a very unstable compound, it will decompose into halogen vapor and tungsten when heated, so that tungsten is deposited on the filament to make up for the evaporated part. Through this regeneration cycle, the cumulative service life of the filament can reach 400-500 hours, which is equivalent to about 4-6 years of work on a car.

Image source: veer gallery

At the same time, since the filament can work at a higher temperature, it can also achieve higher brightness, higher color temperature and higher luminous efficiency. Since it is still an upgrade based on incandescent lamps, the halogen lamp light is similar to the incandescent lamp in terms of luminous color, both of which are yellowish amber platinum, and have better penetration effect in rainy and foggy environments. Due to the low price of halogen lamps, it is still the choice of most family cars until now.

Part 3

High-pressure gas discharge lamp sounds cool

A high-pressure gas discharge lamp is a lamp that uses high-pressure gas instead of tungsten filament to encapsulate it in a quartz glass tube, and uses high-voltage current to activate the high-pressure gas to produce arc discharge. Common high-pressure gas discharge lamps include mercury lamps, sodium lamps, and xenon lamps. Xenon lamps are generally used in car lights. In the 1990s, the car light manufacturer Hella introduced the technologically mature xenon car lights to the market. Since there is no need to heat the tungsten filament at high temperature, xenon lamps can provide more stable lighting output than halogen lamps, and the light intensity of xenon lamps is three times higher than that of halogen lamps, but the energy consumption is only two-thirds of that of halogen lamps, only about 35 W.

Image source: Photographed by the author

Moreover, the light color of xenon lamps is almost the same as that of daylight, which is a dazzling bright white, creating a better visual experience for drivers. These advantages and features of xenon lamps have greatly improved driving safety and comfort. More importantly, the theoretical life of xenon lamps can reach 3,000 hours, which is significantly higher than that of halogen lamps. Based on the above advantages, the use of xenon lamps is increasing day by day, especially becoming a common lamp type for mid-to-high-end cars.

Part 4

Powerful LED light

LED lights use light-emitting diodes as light sources. After current passes through the semiconductor, electron holes recombine to emit light. Due to cost reasons, they are only equipped on higher-end models. Compared with all the above types of lights, LEDs have the lowest energy consumption and the longest service life, with a general lifespan of up to 50,000 hours.

The light color of LED is roughly the same as that of xenon lamp, which is bright white like daylight. However, unlike xenon lamp, which needs 3-4 seconds to turn on, LED can be lit instantly. Therefore, when LED is applied to turn signal lamp and high brake lamp, it can meet the emergency response needs during vehicle driving. In addition, the light source can be processed into any shape, which has the advantages of large styling space and strong sense of technology.

Although LED headlights have the best overall performance among the three types of car headlights, they are also the most expensive. Therefore, in addition to being used as headlights on some high-end models, they are mainly used as daytime running lights.

Image source: Photographed by the author

The specific choice of headlights for your car should be determined according to your own driving conditions. If you usually drive in the city, ordinary halogen headlights are sufficient, and because of their yellowish light color, they have better penetration and recognition in rainy and foggy environments. If you often drive in the suburbs or on roads with poor street lights, xenon lamps can make up for the shortcomings of optical fibers and road conditions because of their higher brightness and relatively affordable prices.

Comparison of different car lights Image source: created by the author

For car owners who pursue driving experience and whose conditions permit, LED lights would be a good choice. However, the brighter the car headlights, the better, because they will affect the vision of the other driver when meeting at night, thus posing a safety hazard.

References:

[1] Yang Lijun, Zhao Yu. A brief analysis of the development of automobile lighting technology and styling[J]. Automobile Practical Technology, 2019(24):3.

[2] Guan Weili. Research on the development of automobile lighting technology based on patent analysis[D]. North China University of Aerospace Engineering.

[3] Yang Zhengbo. The "past", "present" and "future" of automobiles[J]. Mathematics, physics and chemistry for middle school students: in line with the textbooks of People's Education Press, 2015(Z1).

[4] Chen Yan. The current status and development prospects of automotive lighting [J]. Lighting and Illumination, 1989(3):3.

[5] Cheng Bo. A brief discussion on the current status and development trend of automotive lighting[J]. Times Auto, 2017(01X):2.

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