The Mercedes-Benz CLS550 uses the 12961 bulb for the front parking light across the 2007-2011 model years.
The 12961 is a Philips part number designating a miniature wedge bulb in the T10 form factor with a W2.1x9.5d base, rated at 12 volts and 5 watts.
The T10 wedge bulb format uses a wedge-shaped glass envelope that seats directly into a socket without a separate metal base, relying on the glass itself to make the electrical connection.
The W2.1x9.5d base designation refers to a standardized wedge base type, where the contact width and pin spacing conform to international bulb base standards.
At 5 watts, the 12961 operates at a low power draw consistent with parking light functions, which are intended for vehicle visibility rather than road illumination.
The same 12961 bulb size applies to the front parking light on the CLS550 both with and without the halogen capsule headlamp configuration for the 2007-2011 model years, indicating no variation in parking light fitment based on headlamp type.