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What do the letters on Xenon bulbs mean?

By 2020-03-18July 25th, 2021Glossary

Anyone dealing with xenon headlights will come across lamp designations that begin with D. Why not X, for xenon? Well, the D stands for “Discharge”. This is the technology by which xenon light works. The D is followed by a number, with the D1 being the newer lamp type compared to the D2. This comes from history. The D2 was the first replaceable xenon lamp. Originally, the non-replaceable light source of BMW’s first xenon headlights was called D1. After a fairly short time, it was no longer allowed to be used for new designs and so its number was freed up for a replaceable further development.


Light Bulb Letter

However, the designations of xenon lamps contain another letter after the number, and R or S. It indicates the basic type of headlight for which the lamp is intended. For example, the D1S is intended for one with lenses. The experts call it a projection system. Its sister D1R provides the light for a lensless headlamp with a large reflector, also called a reflector system. So the R stands for a reflector. Only – what does the S abbreviate? It stands for the shutter. This shutter moves so far in front of the lamp during dimming that dipped beam light is produced.

The S and R lamps are therefore different and are not interchangeable. To prevent this from happening accidentally, the bases are designed differently.

Xenon-based discharge lamps can be roughly divided into three large groups:

  • For H1-H27, HB3-HB5 bases, which are installed in retrofitted regular headlights of various vehicles.
  • Bi-xenon headlamps with H4M, HB1M, H13M, and others with the letter “M” of the same designation. Their purpose is to replace halogen lamps which are both driving and dipped beam sources.
  • Xenon lamps with D1S, D1R bases – D4S, D4R. These light sources are installed by the manufacturer in the headlights right from the assembly line.
David Muench (Carnes Mechanical)

David Muench (Carnes Mechanical)

Hey, I’m David. I’ve worked in a cars store for 6 years. I write reviews and guides, helping people to choose the most suitable technicals and best product for them. I’m happy to finally share my knowledge of the industry here, on CarnesMechanical.

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