The Lexus IS250 back up light uses a 921 bulb size for the lighting component located at the rear of the vehicle. Data for the specified bulb covers the range from 2006 to 2009.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Lexus IS250 uses two distinct back up light bulb positions across the 2006-2009 model years: a standard back up light and an inner back up light, each requiring a different bulb size.
The 921 bulb is specified for the standard back up light position on the IS250 for all four model years covered, making it the primary bulb in this application.
The 921 is a T15 wedge-type bulb rated at 12 volts and 16 watts, conforming to ANSI standards applicable in both the United States and Canada.
The T15 designation refers to the bulb's wedge base form factor, which uses a plastic wedge base rather than a metal pin or bayonet fitting, allowing direct insertion into a compatible socket.
The inner back up light position on the IS250 requires a 3057 bulb across the 2006-2009 model years, a specification that differs from the outer position.
The 3057 is a T25 dual-filament wedge bulb rated at 12 volts with a wattage of 27W on the high filament and 7W on the low filament, also conforming to ANSI standards for the US and Canadian markets.
The dual-filament construction of the 3057 means the bulb contains two separate filaments within a single envelope, each operating independently at different wattage levels.
Because the 921 and 3057 differ in both physical size and electrical characteristics, the two bulb types are not interchangeable between the standard and inner back up light positions on the IS250.
Both bulbs share the same 12-volt operating voltage, which is consistent with standard 12V automotive electrical systems found in passenger vehicles of this type.
The ANSI classification on both bulbs indicates adherence to a standardized specification governing filament, base, and electrical properties, which allows for cross-brand substitution within the same ANSI number.