The Buick LaCrosse uses two distinct bulb types across its tail light assembly for the 2005-2009 model years: the 194 for the inner tail light position and the 3057 for the outer tail light position.
The 194 is an ANSI-standardized miniature wedge bulb in the T10 form factor, rated at 12V and 3.78W, making it a low-wattage unit suited for secondary lighting roles such as the inner tail light.
The T10 designation refers to the bulb's tubular glass envelope width, expressed in eighths of an inch, placing it among the smaller wedge-base bulbs in common automotive use.
The 3057 is an ANSI-standardized dual-filament wedge bulb in the T25 form factor, operating at 12V with a 27W high filament and a 7W low filament, which allows it to serve both brake light and tail light functions within a single unit.
The dual-filament design of the 3057 is a defining characteristic of the outer tail light position on the LaCrosse, as the higher-wattage filament activates under braking while the lower-wattage filament remains active as a running light.
Both the 194 and 3057 conform to ANSI standards recognized in the United States and Canada, indicating consistent fitment expectations across North American market vehicles.
The wedge-base construction shared by both bulb types means neither uses a separate metal base or bayonet pins; instead, the glass envelope itself is shaped to lock directly into the socket.
Substituting a single-filament bulb for the 3057 in the outer tail light position would result in the loss of either the brake or running light function, as the dual-filament design is integral to that circuit's operation.
The 194 and 3057 are not interchangeable with each other due to differences in physical size, wattage, and filament count, and each is specific to its designated socket in the LaCrosse tail light assembly.