Opel Kadett Dome Light Bulb Size

The Opel Kadett dome light requires bulb size 57 or 257 depending on the specific configuration of the interior lighting system. Data for the lighting components covers the range from 1970 to 1972.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1972	57
1971	257
1970	57

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA9s base. 12V, 1W.	57
ANSI standard (US & Canada). Festoon or BA9s base instrument bulb. 12V, 2W.	257

Other Locations

Additional Notes

The BA9s base is a miniature bayonet cap fitting with a 9mm cap body, commonly used in small indicator and interior lighting applications across North American market vehicles.
The Opel Kadett uses the 57 bulb for the dome light in the 1970 and 1972 model years, while the 1971 model year specifies the 257 bulb instead.
Both the 57 and 257 are ANSI-standardized bulbs rated for the North American market, covering the United States and Canada.
The 57 bulb operates at 12V and 1W, making it a low-output single-filament type suited to interior courtesy lighting rather than high-visibility applications.
The 257 bulb operates at 12V and 2W, doubling the wattage of the 57, and is compatible with either a festoon or BA9s base configuration.
The festoon base type referenced in the 257 specification describes a cylindrical bulb held in place by contact at each end rather than by a socket, a format common in dome and map light housings.
Because the 257 accepts either a festoon or BA9s base, it covers a broader range of socket types than the 57, which is limited to the BA9s base only.
The wattage difference between the 57 and 257 means the two bulbs are not directly interchangeable without accounting for the electrical load tolerance of the vehicle's lighting circuit.