The Lexus IS300 back up light utilizes bulb size 921 or 7440 depending on the specific version required for the vehicle. Data for the bulb sizes covers the range from 2001 to 2016.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 921 bulb follows the ANSI standard for the US and Canadian markets. It is a T15 wedge-type bulb rated at 12 volts and 16 watts.
The 7440 bulb also follows the ANSI standard for the US and Canadian markets. It is a single-filament T20 wedge-type bulb rated at 12 volts and 21 watts, drawing notably more wattage than the 921.
Wedge-type bulbs, such as the T15 and T20, use a plastic base that wedges directly into the socket without a separate metal connector, which is a common design in automotive backup lighting applications.
The Lexus IS300 (2016) uses a 921 bulb for the back up light, while the 2001 model year uses the higher-wattage 7440 bulb for the same position.
The 921 and 7440 are not interchangeable. They differ in bulb family, physical size, and wattage, meaning a direct substitution between the two would be incompatible with the intended socket and circuit.
For the Inner Back Up Light on the Lexus IS300, the 2016 model year uses a 921 bulb. The 2017 model year also uses a 921 bulb, but only for vehicles produced up to October 2016, indicating a mid-cycle specification that corresponds to a production date rather than a calendar year alone.