In 1989 Philips developed the D1 lamp, which was later also offered by Osram . From 1991 gas discharge lamps (Bosch Litronic) were available as xenon lights for the 7 Series BMW , initially only as low beam. The D2 lamp has been used in the Audi A8 and the BMW E38 since 1994 ; it is still produced today in a slightly modified form. Since 1999, first in the Mercedes-Benz CL , there have also been xenon high beams in so-called bi-xenon headlights . The same lamp is used for the low beam and high beam, whereby a diaphragm is folded out of the beam path for switching, thus enabling high beam. There are also xenon headlights with integrated cornering lights , which are intended to achieve improved illumination when cornering thanks to horizontally movable lenses.
Distribution and availability
In 2007, 30% of the new passenger cars in Germany were equipped with xenon headlights, according to the 2008 DAT report, around 15% of the total number of cars. In addition to xenon and halogen headlights, they are still state of the art and account for a high proportion of new registrations. In 2015, 38% of new registrations, 20% of used vehicles and 24% of the vehicle fleet were equipped with xenon lights. The equipment rate in the lower vehicle classes is lower than in the upper class.
Between two tungsten - electrodes of the xenon arc lamp burns a concentrated arc . The extremely small combustion chamber - a glass bulb made of quartz glass - contains a xenon gas filling under high pressure as well as mercury (see below for differences in lamp categories ) and metal halides - less than a milligram in total. The metal halides are present for color rendering enhancement. The xenon gas is for a considerable luminous flux shortly after ignition and u. a. responsible for quickly starting the lamp, which plays an important role in traffic. In conventionally used metal halide lamps, argon is usually used as the starting gas, with which, however, it takes several minutes to deliver a significant luminous flux or to achieve the entire amount. Strictly speaking, the xenon burner is therefore a combination of a xenon gas discharge lamp and a metal halide lamp . Newer versions do not contain any mercury in the filling.
Double xenon headlights are technology without a flap; the low beam and high beam each consist of a burner and separate lenses or reflectors. Vehicles with two double xenon headlights therefore have four burners and therefore four ballasts.
The shelf life of xenon lamps is around four times that of halogen lamps. Since xenon lamps are gas discharge lamps, however, defective burners cannot be identified by a burned-out filament.
So that the gas discharge lamp can be used on motor vehicles in traffic, the known slow light start-up must be accelerated. The process required for this can be described in three phases:
- Ignition: With a high voltage pulse - similar to a spark plug - a spark is generated that ionizes the originally electrically non-conductive gas and thus creates a conductive tunnel between the tungsten electrodes. Through this tunnel, the electrical resistance becomes small and current flows between the electrodes.
- Start-up phase: The lamp is operated with a controlled overload. As the arc is operated with higher power, the temperature in the bulb rises rapidly and the metal halides that are present begin to evaporate, which changes the color of the light. The vapor pressure in the lamp and the light output increase. The resistance between the electrodes also decreases; the EVG control unit recognizes this and automatically switches to continuous operation.
- Continuous operation: All metal halides are in the vapor phase, the arc has reached its final shape and the light output has reached its target value. The electrical power supplied is now stabilized so that the arc does not flicker.
Technical details of a xenon lamp require an electronic ballast. These ballasts are designed as control devices for 12 and 24 V electrical systems and can operate burners with 25, 35 or 50 W. A voltage pulse of up to 25,000 volts is used to ignite the lamp, also known as the burner . A period of up to 15 seconds may be necessary before the full luminous flux is achieved. The approval criteria for motor vehicles require that at least 25% of the target luminous flux is achieved after 1 second and at least 80% of the nominal luminous flux after 4 seconds after switching on without delay (ignition). With a warm start, 80% of the target luminous flux must be achieved after just one second after instantaneous ignition. It can take up to 30 seconds until the operating color temperature is set.
The arc increases the pressure of the xenon inert gas filling in a burner from around 20 bar (2 MPa) to up to 100 bar (10 MPa) during operation. In normal operation, the lamp is often operated with around 85 volts at 400 Hertz square wave . Newer mercury-free lamps operate at around 42 volts. The electrical operating parameters depend on the total operating time (service life) and the condition of the lamp (cold, warm, hot). The coordinates in the CIE standard valence system of a lamp (color location, temperature) change with increasing overall lamp life. The UV components generated during ignition are filtered through a UV-absorbing layer or doping of the burner in order to avoid damage to other components (e.g. polycarbonate lenses). The ballasts generate an alternating voltage from the vehicle electrical system using power electronics . The discharge current of the light plasma is controlled by them - regardless of the supply voltage. The efficiency of these ballasts is around 90%. With the so-called plug starters, the ignition unit is as close as possible to the lamp unit to avoid EMC problems.
Comparison between halogen lamp and xenon light
Motor vehicle xenon lamps are line emitters (see also light spectrum ), the spectral lines of which, however, almost merge into a continuum due to pressure broadening and additives. Some lines are also in the ultraviolet range. The mixture of the lines results in the apparent color - it is bluish than the light from halogen filament lamps. Halogen lamps emit a continuous spectrum that extends far into the infrared range; a normal incandescent lamp emits around 85–95% of its output as heat, only 5–15% is available as light (→ incandescent lamp , halogen incandescent lamps are somewhat more efficient in this regard). The light from a xenon lamp appears colder than that of an incandescent lamp due to its higher color temperature , but is brighter despite the lower power consumption. Newer, low-mercury lamps also contain sodium, which leads to a lower color temperature and makes the light appear warmer.
Halogen bulbs sold with the additional designation “Xenon” either have a color filter ( interference filter ) vapor-deposited onto the bulb to make the light appear bluish, or the glass bulb itself is made of blue glass in order to imitate the higher color temperature of xenon discharge lamps. By cutting the spectrum to include long-wave components, the overall light yield is somewhat reduced.
Differences in lamp categories
Xenon lamps are divided into the ECE categories D1, D1S, D1R, D2S, D2R, D3S, D3R, D4S, D4R and D-H4R. The abbreviation D stands for Discharge (discharge), the following point for the respective development version. Burners with the specification DxS are used in headlights with projection systems. They have a clear glass bulb. Burners with the specification DxR are used in reflector headlights and have an opaque print (pinstrip - also known as a shadow coating ) on the glass bulb. It serves to guarantee the officially prescribed light distribution.
- D1 burners have an integrated ignition part.
- D2 burners only consist of the socketed burner itself.
- D3 and D4 burners are mercury-free versions of the D1 and D2 burners
It is not possible to replace D1 or D2 burners with D3 or D4 burners, as these require a different operating voltage. Ignition is usually possible, but D3 and D4 burners have an operating voltage of 42 V and, in contrast, D1 and D2 burners have an operating voltage of approx. 85 V with the same output. This doubles the required operating current, for which the ballasts of D1 and D2 burners are not designed. To avoid confusion, D3 and D4 torches use a different lamp socket.
Xenon lamps with the designation D1 are the first xenon lamps to be developed. Only these, in contrast to all other development stages, do not have an outer glass bulb protecting the discharge tube. All further developments of this type have a UV protective flask. They are also much more stable in terms of their design. The old D1 is very often confused with today's D1 S / R burners, which contain an integrated ignition module. When we speak of a D1 lamp today, we usually mean the current design with an integrated igniter.
- Brighter light: Xenon lamps achieve significantly higher luminous flux than conventional halogen lamps (H7 = max. 1500 lm , D2S xenon (color temperature 4200 K ) around 3200 lm).
- Lower energy consumption: Xenon lamps have a lower power consumption in continuous operation (35 watts compared to 55 watts for conventional halogen lamps , e.g. H4 or H7). If the light is switched on for 30% of the engine running time , there is a reduction in CO 2 emissions of around 1.3 g / km. Xenon lamps also have a three-fold higher light output (D2S approx. 91 lm / W compared to H7 approx. 26 lm / W).
- longer service life : the average service life of a xenon lamp is 2000 hours compared to an H7 halogen lamp with 450 hours. This average service life is determined in Germany using a test cycle defined by the KBA , which is intended to simulate the conditions of use of the lamp in road traffic.
- higher luminance: The luminance of a xenon lamp is around three times as high (D1S / D2S approx. 90 Mcd / m², as with H7 with about 30 Mcd / m² / Mcd = Mega Candela ). The light emitting area is smaller for the same luminous flux, and the light source heats up less. This enables more compact designs of the headlights (ellipsoid reflectors and converging lenses).
- Daylight-like light color, higher color temperature than incandescent light - blue light makes you livelier and increases the ability to concentrate.
- contrast-enhancing effect in good visibility
- The acquisition costs for xenon light often exceed - depending on the vehicle use - the fuel costs saved due to the improved efficiency.
- With xenon light, the system complexity is significantly higher due to the necessary automatic headlight range control, the headlight cleaning system as well as the ballast and ignition unit compared to halogen light and therefore also causes higher replacement part costs.
- Maintenance and replacement of lamps and ballasts should be left to qualified persons, especially because of the risk of electric shock, as special safety precautions are necessary for this.
- In particular, if the headlights are incorrectly adjusted, oncoming traffic can be more dazzled than with other headlights. An automatic headlight range control is prescribed for xenon systems , but this has no influence on a possibly incorrect basic setting of the headlight that can result from changing the burner. Due to the higher luminance of the xenon headlights, compared to halogen headlights with a corresponding road layout (on hilltops and as a result of the asymmetrical light cone in right-hand bends) but also with the correct setting of the headlights, oncoming traffic is more dazzled, as the automatic headlight range control of older systems does not take the course of the road into account (see Intelligent Light System ).
- The color temperature of the light can change to blue if ignited frequently.
- The light intensity decreases more strongly with increasing operating time (aging) than with a halogen lamp, but the luminosity is then still twice as high as that of a halogen lamp. In detail: While the light intensity of incandescent lamps at the end of their service life (after approx. 450 hours for an H7) is reduced to around 80% (for an H7 from around 30 to 24 Mcd / m²), it drops after approx. 2000 hours for xenon lamps to approx. 50 Mcd / m².
- Increased environmental pollution from mercury (if contained) and electronics, since the problematic ingredients can only be recovered with great effort or not at all. Although two leading manufacturers, Philips and Osram , offer mercury-free xenon lamps, not all vehicle manufacturers use them.
- increased space requirement
- In fog and poor visibility, the high proportion of blue has a negative effect on contrast and visibility, since short-wave light is more strongly scattered by fog and haze than long-wave incandescent light.
Discussion about xenon light
The use of xenon light is controversial, also due to the higher acquisition costs both when buying a new car and when replacing defective light sources. However, the latter costs are put into perspective by a significantly longer service life compared to halogen lamps. The higher light output, the larger illuminated area and the contrast-enhancing effect in good visibility are advantages that increase traffic safety, but initially only benefit the driver and are only standard in a few vehicle models.
According to a study by TÜV Rheinland, widespread use of xenon light would prevent 50% of serious accidents at night on country roads and 30% of serious accidents on motorways (and thus 18% of fatalities). This study is based on official figures from the Federal Highway Research Institute, but was commissioned and financed by an initiative of European lighting manufacturers without this fact being openly disclosed in the published material. It was not determined whether, and if so, how many additional accidents due to glare could be expected.
When measuring above the headlight axis, xenon light must not dazzle more than conventional halogen light. If the headlights are set incorrectly or in certain driving situations (driving over a hilltop or a bump or if the xenon high beam is inadvertently switched on in oncoming traffic), the glare effect is significantly higher than with halogen headlights. An oncoming driver usually finds this uncomfortable. Since a higher luminous flux of the luminaire means an increased glare effect on wet roads, any improvement from the driver's point of view is at the expense of the oncoming.
The Traffic Expert Day recommends xenon light for more safety in road traffic.
Regulations for retrofitting in motor vehicles
- The gas discharge lamp must comply with ECE regulation 99.
- The headlight must comply with ECE regulation 98.
- The installation of the headlight on the motor vehicle must comply with ECE regulation 48. Automatic headlight range control and a headlight cleaning system are required for light sources with more than 2000 lumens. This applies to conventional (35 W) xenon, but also LED headlights , which, due to technology, have a wider power range. The 35 W lamps of the D1, D2, D3 and D4 standards emit a luminous flux of> 2000 lm. A 25 W D8 / D5 lamp, on the other hand, remains below this threshold.
- The headlight cleaning system must comply with ECE regulation 45.
- For high and low beam, the regulations according to
Notes on retrofitting:
The following applies to all lighting equipment on motor vehicles: The type of light source (e.g. incandescent lamp, halogen lamp, xenon lamp, LED) is always part of the type approval of a headlight. It follows:
- The gas discharge lamps may only be used or used in type-tested and approved headlights.
- Fitting a halogen headlight with gas discharge lamps (e.g. D2S, D2R) with retrofit sets is not permitted and leads to the expiry of the vehicle's operating license and thus to the loss of insurance cover.
- For the reasons mentioned above, only the retrofitting of type-approved headlights that have been approved in accordance with ECE regulation 98 is permitted. In addition, the "Regulations for installation in motor vehicles" listed above must be observed. The StVZO does not play a decisive role in vehicles that are approved according to the EC, but the guidelines listed in the appendix to the StVZO are decisive.
- Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden 2003, ISBN 3-528-23876-3
- Robert Bosch (Ed.): Autoelectronics Autoelectronics. 5th edition. Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-528-23872-8
- DAT-Report 2016. Deutsche Automobil Treuhand, January 27, 2016, accessed on April 15, 2019 .
- Color temperature and temperature appearance of a color seem to be in contradiction. A bluish white has a higher color temperature than a more yellow one, but the color impression is colder.
- Mercury-free high-pressure gas lamps for use in automobile headlights ( Memento from December 15, 2007 in the Internet Archive )
- blue light to help alertness ( Memento of December 8, 2008 in the Internet Archive )
- Spiegel Online : TÜV STUDY: Xenon light drastically reduces the risk of accidents
- Lifesaver Xenon Light, TÜV Rheinland Study ( Memento from February 8, 2009 in the Internet Archive )
- Boocompany ( Memento from October 5, 2010 in the Internet Archive ): TÜV Rheinland operates covert PR for the automotive supplier lobby
- Regulation No. 45: Uniform provisions concerning the approval of headlamp cleaners and of power-driven vehicles with regard to headlamp cleaners. (PDF) In: unece.org. Accessed March 14, 2018 (English).
- Jana: Tuning: Headlights - Changes to the Car 2019. In: bussgeldkatalog.org. November 19, 2015, accessed May 3, 2019 .