The past and present life of automobile headlights (1)

2020-04-14 10:58:21

Tungsten and halogen lamps

Although the initial performance of the light bulb is not satisfactory, the power age is still an irresistible historical flood. In 1913, the spiral tungsten filament lamp replaced the original carbon filament lamp, the irradiation intensity increased by 50%, the service life and reliability were improved, which created the conditions for being installed on the bumpy car.

Since the original car didn't have battery, the first vehicle to use light bulb was electric vehicle (now defined as new energy vehicle in China, electric vehicle is not "new", the birth of electric vehicle even earlier than petrochemical fuel vehicle). At that time, the lead-acid battery on the electric vehicle could provide long-lasting and stable power for the electric bulb. Therefore, most electric vehicles at the beginning of the last century were equipped with the electric bulb as the lighting equipment.

However, with the improvement of lighting brightness, it not only lights up the front of the car, but also causes the opposite glare, which seriously affects the driving safety. At that time, the structure of the lamp was simple, only the bulb and the spotlight bowl to increase the illumination could not control the illumination angle and range of the lamp, so at that time, the driver could only stop when there was a meeting in front of the vehicle, and it was quite troublesome to go to the front of the vehicle to lower the fixture of the lamp.

In 1915, guide lamp Co., Ltd. introduced the first automobile lamp equipped with near and high beam adjustment considering the dazzling of passing cars, but the lamp system involved in it can only adjust the level of light exposure, not the range of light exposure. Then, Corning company developed a lamp glass cover with beam adjustment function. The glass cover controls beam diffusion through optical design, making the light beam more concentrated and reducing glare.

But this way can not achieve adjustment, so the concept of low beam, high beam gradually formed. The low beam light has a low illumination angle and a small range. When there is good road lighting, it helps the driver to see the road conditions at a short distance at the front of the vehicle without "shaking" to the opposite vehicle. The high beam light has a large illumination area, a long illumination distance and a higher light intensity, which is suitable for lighting in all dark road conditions, but it will cause a strong glare to the vehicle. Therefore, the high beam light must be turned off when meeting the vehicle.

OSRAM is the first company to design the headlamp bulb with the function of high and low beam exchange. This design is very clever. It will be responsible for far and low beam lighting two filament integrated in a lamp holder. The power of the filament responsible for the driving beam is high, which is set on the focus of the reflecting bowl, and the light is evenly illuminated to the large range in front through reflection; while the passing beam filament is set in front of the focus, and the reflection angle is inclined to the ground.

The driver can control the illumination and extinction of the far and low beam filaments in the vehicle: when facing the vehicle, the high beam filaments will be off; when facing the vehicle, the two filaments will be on at the same time. This kind of light bulb is the ancestor of modern H4 light bulb.

At that time, the optical design was not perfect. In order to improve the illumination and increase the irradiation range, there were complex edges and spirals on the headlamp cover. Therefore, the headlamp cover we saw on the old cars was not completely transparent. With the improvement of bulb technology, a series of parts are added to control reflection and refraction, such as refracting umbrella, lens, shutter, etc. the coating materials and optical structure of the reflecting bowl are also optimized to better control the illumination range and shape of the light. Therefore, the large lampshade of modern automobile becomes clear and transparent (once known as "crystal diamond headlight"), so that we can control the reflection and refraction from the outside Look through the structure of the headlight.

With the development of technology, the disadvantages of ordinary tungsten filament lamp (incandescent lamp) are more and more prominent, such as weak light, low color temperature, and blackening after long use. Therefore, halogen bulb appeared in the 1950s. Now more than 90% of vehicle bulbs are halogen lamps.

The halogen bulb still uses tungsten wire as the light source, but it is filled with halogen (a mixture of bromine and iodine). When the filament heats up, the tungsten atoms are evaporated and move towards the glass tube wall. When approaching the glass tube wall, the tungsten vapor is cooled to about 800 ℃ and combined with the halogen atoms to form tungsten halide (tungsten iodide or tungsten bromide). The tungsten halide continues to move towards the center of the glass tube and returns to the oxidized filament. As tungsten halide is a very unstable compound, it will be re decomposed into halogen vapor and tungsten after being heated, so that tungsten is deposited on the filament to make up for the evaporated part.

Through this recycling process, the service life of the filament is not only greatly extended (almost four times as long as that of the incandescent lamp), but also because the filament can work at a higher temperature, thereby obtaining a higher brightness, a higher color temperature and a higher luminous efficiency.