Skip to main content

The lamp designations for xenon headlights range from D1 to D4. Lamp type numbers identify the technology by which they work, and in this case it’s “Discharge”. The first letter represents year of production (a lowercase ‘l’), then comes an Arabic number between 1-9 that corresponds with what specific brightener is being used; 4 stands for emitters containing potassium hydroxide (Khell), 6 uses rubidium aluminum encouraging electron flow through vacuum tubing while 3 relies heavily on lithium aluminium hydride during discharge process


Light Bulb Letter

xenon lamps come in two types, based on how they’re designed to emit light. One is a projector system with lenses that projects an image into the face of drivers traveling ahead; this type features “R” or S after their number depending if you want reflector heads for better visibility during bright conditions (e). The other form factor generates less glare by bathing nearby objects in darkness while still providing enough illumination needed near Stop & Shop stores at night– these have shutter mechanisms which move between open positions blocking out direct exposure from sources like streetlights outside your vehicle
The letter ‘r’ stands meaningfully different things depending upon what function it serves within each model.

Xenon lamps contain an additional letter after the number, and R or S. The lamp’s type is indicated by this second digit; 1R means it has a reflector system while 2Ds refer to lenses for your headlight projectors!
This information might be interesting if you want more details about how these lights work–but what does “S” stand for? It turns out that ‘shutters’ move farther than regular openings during dimming (to block some light) so they produce dipped beam output instead of projected illumination as we’d expect from our English word “projection.”

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.

Leave a Reply