Alfa Romeo 4C Headlight Bulb Size

Additional Notes

• The Alfa Romeo 4C uses two distinct headlight technologies across its 2015-2020 production run: halogen capsule headlamps fitted with the 9012 bulb, and HID headlamps fitted with the D5S bulb. Both technologies serve dual duty, with the same bulb type handling both high beam and low beam functions within each headlamp system.
• The 9012 is a single-filament enhanced halogen bulb operating at 12V and 55W, built to the ANSI standard used in the United States and Canada. It uses a PX22d base, which is a push-and-twist locking mount common to enhanced halogen capsule designs.
• The D5S is a high-intensity discharge xenon bulb operating at 12V and 25W, conforming to the ECE standard used in Europe and internationally. It uses a PK32d-7 base and belongs to the low-voltage compact HID category, which requires a ballast to generate the high-voltage arc needed for ignition.
• Despite the lower wattage of the D5S relative to the 9012, HID technology produces significantly greater luminous output per watt, meaning the 25W D5S generates more usable light than the 55W halogen alternative.
• The 9012 and D5S are not interchangeable. They use different base types, different operating technologies, and different electrical systems. A vehicle equipped with HID headlamps requires the D5S and its associated ballast hardware, while a vehicle equipped with halogen capsule headlamps requires the 9012.
• The 2019 Alfa Romeo 4C specifications list only the 9012 for both high and low beam positions, with no D5S entry for that year, indicating that the HID headlamp configuration was not listed as an available option for the 2019 model year.
• The 9012 bulb is sometimes referenced in relation to the 9011 and HIR2 designations, as these share the same PX22d base family. However, wattage and filament specifications differ between them, and substitution without confirming exact compatibility is not advised.
• Because both the high beam and low beam positions share the same bulb type within each headlamp system on the 4C, the headlamp assemblies are designed around a single-bulb dual-function configuration rather than separate dedicated bulbs for each beam mode.