Basic principles of car lighting technology

Unit: lumen [lm]

Luminous flux F is the term used to describe the complete light output radiated from a light source.

Unit: candela [cd]

The luminous intensity is the portion of the luminous flux radiating in a specific direction.

Unit: lux [lx]

Illuminance E specifies the ratio of the impinging luminous flux to the illuminated surface.

Illuminance is 1 lx when a luminous flux of 1 lm impinges an area of 1 m² evenly.

Unit: candela per square meter [cd/m2]

Luminance L is the impression of brightness the eye has from a luminous or illuminated surface.

Bulbs (vacuum incandescent lights) are temperature radiators, since the tungsten filament is made to glow by the addition of electrical energy.

As already mentioned, the light output of a standard bulb is comparatively low. In addition, the vaporised tungsten particles that can be seen clearly as black marks on the bulb reduce all the technical lighting values, and the service life of such bulbs is relatively short.

The halogen bulb offers significant advantages in comparison to classic bulbs. Adding small quantities of halogen atoms, e.g. iodine, can reduce the blackening of the light bulb.

Thanks to the so-called "cycle process", halogen bulbs can be operated at higher temperatures with the same service life and thus offer greater efficiency.

Halogen bulbs with a blue finish have also been available for some time now. In contrast to conventional halogen bulbs, these bulbs produce a bluish-white light (up to 4000 K) and are thus closer to the colour of daylight. The light appears brighter and more contrasting to the eye. This should help drivers to drive for longer without fatigue. This impression is subjective, however.

Those who want maximum light output are better served by the +30/50/90 bulbs.

Up to now, lights with amber-coloured glass bulbs have been used as direction indicators. Magic Star indicator bulbs are also available for design-oriented drivers. When switched off, they are barely visible in the silver reflector. The characteristic amber light is only radiated at the usual brightness once they are switched on.

The application of several interference layers on the glass bulb of the light quenches certain shares of the light spectrum radiated by the filament. Only the amber share penetrates the layers and then becomes visible.

Gas discharge lamps generate light according to the physical principle of electrical discharge. Through the application of an ignition voltage from the ballast (up to 23 KV in 3rd generation HELLA ballasts), the gas between the lamp electrodes (filled with the inert gas xenon and a mixture of metals and metal halides) is ionized and made to glow with the aid of a light arc.

During the controlled feeding of alternating current (at approx. 400 Hz) the liquid and solid substances evaporate due to the high temperatures. The lamp only achieves its full brightness after a few seconds when all the components have been ionized.

To prevent destruction of the lamp through uncontrolled increases in current, the current is limited by a ballast. Once the full light output has been reached, an operating voltage (not the ignition voltage) of only 85 V is necessary to keep up the physical process. Luminous flux, luminous efficiency, luminance, and service life are significantly better than with halogen bulbs.

Gas discharge lamps are categorized according to their respective development version: D1, D2, D3, and D4. The "D" stands for "discharge". There are some major differences between the generations. The D1 lamps, for instance – the original xenon bulbs – have an integrated ignition section. D2 lamps, on the other hand, only consist of the socketed burner itself and, unlike all other development versions of automotive gas discharge lamps, have no exterior protective glass bulb around the discharge tube. All further developments have a UV protection bulb and are much more robust in their design.

The old D1 is often mistaken for the current D1 S/R lamp with integrated ignition module. Further developments of the D1 and D2 lamps, the D3 and D4 lamps, are more environmentally compatible, as they use no mercury. Due to different electrical parameters (42 V instead of 85 V arc voltage, with identical output), the D3 and D4 lamps cannot be used with the control units for D1 or D2 lamps.

• Name of the manufacturer
• 6 or 6 V, 12 or 12 V, 24 or 24 V stands for the rated voltage in compliance with ECE regulation 37.
• H1, H4, H7, P21 W stands for the international category description of ECE-standardised bulbs e.g. 55 W.
• E1 indicates which country the light source has been tested and approved in. "1" stands for Germany.
• "DOT" means that it is also approved for use on the American market.
• "U" stands for UV-reduced bulbs, according to ECE. The bulbs are used in headlamps with plastic cover lenses, for example.
• The approval mark granted by the appropriate authorities, e.g. E1 (Federal Department of Motor Vehicles in Flensburg), is inscribed on the bulb and is either 37 R (E1) + a five-digit number or only (E1) + a three-digit number (sometimes alphanumerical codes, see illustration).
• Most bulbs have a coded manufacturer's mark. This makes traceability to the manufacturer possible.
• Since not all bulbs have enough room for the markings, the legislator prescribes only the following obligatory information: Manufacturer, output, inspection tag, and approval mark.

• Mechanical loads through impact and vibrations
• High temperatures
• Switching-on process
• Voltage spikes
• Excessive on-board voltage
• High luminance due to extreme
• filament density

• Filling pressure
• Filling gas

• Xenon headlights require a high voltage for ignition, which is why the ballast voltage supply connector should always be removed before any work is carried out on the headlamps.
• When using a new bulb, never touch the new glass bulb since fingerprints will be burnt on and make the bulb opaque.
• If a xenon bulb breaks in a closed room (workshop), the room should be ventilated to prevent a health hazard due to toxic gases. D3 and D4 xenon lamps no longer contain mercury and are therefore more environmentally compatible.
• Standard filament and halogen bulbs do not contain any materials which are problematical from an environmental point of view, and can be disposed of with normal household waste.
• Xenon bulbs are special waste. If the bulb is faulty but the interior glass bulb is still intact, it has to be disposed of as special waste since the gas/metal vapor mixture contains mercury and is thus extremely toxic when inhaled. If the glass bulb has been destroyed e.g. in an accident, the xenon bulb can be disposed of with normal household waste since the mercury will have evaporated.
• In D3 and D4 xenon lamps, the mercury was replaced with non-toxic zinc iodide. These bulbs can be disposed of with normal household waste.
• The waste code for disposal is: 060404.
• There are no separate tips for LEDs, as these usually cannot be replaced.

Our bulb configuration tool helps you find the right bulb quickly and easily. In order to find out which bulbs are compatible with your vehicle, select the vehicle make, vehicle class, and year of construction.

This way to the bulb configuration tool.