Xenon headlights explained – ballasts, causes of faults, legislation

Xenon headlights provide substantially more light on the road than classic halogen headlamps. They increase safety when it is dark and are now found in almost all vehicle classes. On this page, find out about the structure of xenon headlights and how they work. You can also find out what causes xenon ballasts to fail, how faults can be found quickly, and how dangerous it is to retrofit illegal xenon headlights.

The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

Bi-xenon headlights module

Xenon headlights are comprised of the gas discharge lamp, the xenon ballast, and the reflection and projector-type system. Bi-Xenon means that high beam and low beam are realised by a projection module. This has the advantage that only one ballast is required. This means that two light distributions with a large luminous flux are realised within the smallest installation space.

Bi-Xenon headlights module: Illumination with good high beam light

Bi-Xenon headlights module: Illumination with Bi-Xenon high beam light

Function

Through the use of a moveable cover, a purely mechanical switch between the light distributions for high beam and low beam is possible. This means that, aside from the actuating mechanics for the cover, there is no additional outlay for a separate headlamp with its own control electronics. The high beam light also reaches further and the areas to the side of the road are illuminated better.

Xenon ballasts

The electronic ballast (E) ignites the inert gas mixture in the bulb with a high-voltage pulse of up to 30 kV (4th generation). It causes a spark to flash over between the electrodes of the bulb. The electronic ballast controls the start-up of the bulb so the bulb reaches its operating phase quickly, and then controls the bulb power to a constant 35 W.

A DC converter generates the required voltage for the electronics and the bulb from the vehicle electrical system. The bridge circuit supplies a 300-Hz alternating voltage to operate the xenon bulbs. Several control and safety circuits are integrated in the device.

Several control and safety circuits are integrated in the device.

The system is switched off within 0.2 seconds in the event of:

A missing or faulty burner
Damaged wiring harness or bulb part
Differential current (fault current) greater than 30 mA; the switch-off time becomes shorter the greater the differential current

To protect the ballast electronics, a counting circuit ensures that a faulty bulb is only ignited seven times. After this, it is switched off.

If the cable connector is removed during operation, the voltage connections are practically voltage-free (< 34 V) after < 0.5 seconds, meaning that there is no immediate danger of electric shock should the warning notice not be complied with.

Properties and differences of the 3rd / 4th generation compared to the 5th / 6th generation

Features	3rd generation	4th generation	5th generation	6th generation (Xenius)
Burner	D2	D2	D1	D1 / D3
Internal igniter	X
External igniter		X
Filtered and shielded version		X
Fully shielded system			X	X
Longer cable possible		X
Improved ignition reliability		X
Laser-welded housing			X	X
All AFS functions integrated			X
LIN communication				X

Ignition module

The different versions meet various limit values in terms of electromagnetic compatibility.
The main differences between the 3rd and 4th xenon generations are an igniter with or without metal shielding and the cable group between the ballast and the igniter which either features shielding or does not have it.

Checking the xenon ballast

Check whether the ballast attempts to ignite the bulb when the light is switched on. The ignition attempts can be clearly heard in the vicinity of the headlamp. If the ignition attempts are unsuccessful, the xenon bulb should be tested by using the bulb from the other headlamp.
If no ignition attempt is carried out, the fuse should be checked.
If the fuse is OK, check the voltage and ground supply directly on the ballast. Voltage must be at least 9 Volts.
If the voltage and ground supply, as well as the xenon bulb, are OK, the cause of the fault is a faulty ballast.

Retrofitting xenon headlights – illegal retrofitting

Xenon headlights look sophisticated and provide the vehicle with a top-class feel. This causes some drivers to upgrade their vehicles with xenon lights. They buy a set with cables, xenon light sources, and ballast, remove the halogen bulb from the headlamp, saw a hole in the cover cap, insert the xenon bulb into the reflector, connect the electronic ballast with the vehicle electrical system, and the xenon headlight is finished. But beware! This procedure endangers other road users because of extreme glare and is illegal: The general vehicle certification is rendered invalid, and insurance protection is restricted. Only complete, type-approved xenon headlight sets including automatic headlamp leveling and headlamp cleaning systems are legal.

Retrofitting xenon headlights – legal foundation

In Europe, only complete xenon headlight systems may be retrofitted. These comprise a set of type-approved headlamps (with identifier E1 on the cover lens, for example), automatic headlamp leveling and a headlamp cleaning system (regulation as per ECE regulation R48 or compliance with national regulations).

Every headlamp is granted its design approval together with the light source (halogen or xenon) used for operation. If the light source is replaced by a different light source that has neither been granted type approval nor has been provided for in the design approval of the headlamp, the design approval is no longer valid, thus invalidating the general vehicle certification (§ 19 StVZO, section 2, clause 2, no. 1). Driving without general vehicle certification leads to restrictions in insurance protection (§ 5, section 1, no. 3 KfzPflVV, German compulsory insurance directive). Those who sell such lighting equipment which has no type approval have to be prepared for damage claims by buyers, too. Because when the seller passes on these parts, they not only guarantee that these may be used for the intended purpose, but they also possibly take over responsibility for the risk of damage as well – to an unlimited amount.

High glare values: Measurements in the lighting laboratory have shown that the active light distribution of a headlamp which was developed for halogen bulbs and is now operated illegally with a xenon light source no longer corresponds to the values calculated originally in any way.
In the case of reflection systems, glare values were measured which exceed the permissible limit values by a factor of up to 100.
The headlamps of these vehicles then no longer have a cut-off line and can also no longer be adjusted. The glare values correspond to those of high-beam headlamps. This endangers other road users massively.