Especially in the dark season - but also on every other day of the year - they are one of the most important safety-relevant vehicle parts: headlights. They are available in various designs and, if a well-known manufacturer has their way, they will soon also be available with projection technology.
The classic headlights of a motor vehicle are halogen headlights. They have a good price-performance ratio, but in comparison to other lights only moderately good illumination on the street. Halogen lamps are divided into classes: H1, H3, H7, H9, H11 and HB3 have only one filament, which is why a lamp for high and low beam must be installed. H4 lamps have a two-filament system and thus two filaments, one of which is used for the high beam and the other is responsible for the low beam.
Most new vehicles are equipped with halogen headlights as standard, only some manufacturers - mostly high-class ones - already use xenon headlights instead of halogen in the basic variant. Compared to xenon headlights, halogen has an undeniable cost advantage. While the technology for xenon headlights is more sophisticated, simple incandescent lamps are used for halogen headlights, which can even be replaced by yourself on many models.
However, the illumination of halogen lamps is significantly worse compared to xenon or LED headlights. The yellowish light often only provides spotty illumination, so that it appears clearly too dark, especially when driving overland. Xenon lights are also clearly superior to halogen headlights when it comes to cornering lights.
Xenon is a chemical element from the group of noble gases. Incidentally, it is the rarest stable element on earth and occurs in low concentrations in the atmosphere from which it is also extracted.
Xenon headlights are based on the principle of the gas discharge lamp: two tungsten electrodes, which have no contact point, are melted into a bulb. The flask is still filled with xenon. If a high voltage is applied to the electrodes, a spark ignites, which ionizes the surrounding gas. This closes the line between the two electrodes, so that a short-circuit current is created. The rise in temperature in the flask causes the metal halides to evaporate, creating an arc which, in continuous operation, reaches its final color and shape when all metal halides have reached the vapor phase. The color temperature of 6.000 Kelvin corresponds to the color of daylight.
Due to the high operating temperatures, xenon lamps require cooling devices and explosion-proof housings. In addition, an electronic ignition unit is required in a ballast in order to deliver the high-voltage pulse required to ignite the xenon light and to achieve control of a light output that is as constant as possible after ignition. This of course increases the cost factor immensely, so that if you equip it with xenon lights, you can expect up to 1.500 euros for the lights only. In contrast to halogen headlights, xenon lamps have a service life that is around four times longer and their enormous luminosity also makes gas lamps a good choice. In terms of brightness, lateral illumination and range, they are clearly superior to halogen lamps.
An alternative to xenon headlights in terms of brightness are LED lights. These are already used in many new vehicles, and they are also very beneficial in hybrid and electric vehicles, as they only use half as much energy as xenon lights.
LED headlights consist of groups of composite LEDs, since individual LEDs have a low light intensity. Since LEDs are very temperature sensitive, heat sinks are required to cool them sufficiently. LED headlights have a similar, and in some cases even better, illumination and brightness than xenon headlights. The first production vehicle to be equipped with LED headlights was the Lexus LS 2007h in 600.
In terms of costs, LED headlights are in the same range as xenon headlights: up to 1.500 euros surcharge can be added for the LED equipment.
Just like xenon headlights, LED headlights also have a color temperature that is similar to daylight. This is very beneficial as it makes drivers less likely to tire.
All types of the above-mentioned headlights can be used in adaptive cornering lights, which are installed in many cars; however, LEDs are used in many models. Overall, the cornering light, as it is installed in new vehicles, has a significant influence on safety: In bends, the radiation almost doubles the field of vision.
In general, when buying a new vehicle, it is important to pay attention to the lighting technology: While halogen lights are cheaper, LEDs and xenon lamps are better in terms of illumination. In addition, thanks to their extremely long service life, LED headlights are environmentally friendly and ideally suited for use in electric and hybrid vehicles.
Source: green car magazine issue II / 2017
Cover picture: Headlight systems in comparison - Copyright Shutter81 @ fotolia.com
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