The Lexus GS450h back up light requires a bulb size of 921 for proper installation and function within the rear lighting assembly. Provided information covers a span of time starting from 2007 through 2015 for the specified vehicle components.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Lexus GS450h back up light system uses two ANSI-standard bulb types across its model years: the 921 and the 3057, both rated for 12-volt electrical systems and standardized for the US and Canadian markets.
The 921 is a single-filament wedge bulb in a T15 form factor, rated at 16 watts. It serves as the back up light bulb across the 2007-2011 and 2013-2015 model years, and also appears in the inner back up light position for the 2007-2011 model years.
The T15 designation refers to the bulb's tubular glass envelope width, expressed in eighths of an inch, making the 921 a relatively compact wedge-base bulb suited to tighter housing spaces.
The 3057 is a dual-filament wedge bulb in a T25 form factor, rated at 27 watts on its high filament and 7 watts on its low filament. It is used exclusively in the inner back up light position on the 2013-2016 Lexus GS450h.
Because the 3057 carries two filaments and the 921 carries one, the two bulb types are not interchangeable despite both using wedge bases. Substituting one for the other would result in either incorrect wattage or non-functional filament circuits.
The 2016 Lexus GS450h inner back up light specifies the 3057 with a production cutoff noted as "To 10/2015," indicating that this fitment applies only to vehicles produced through October 2015 within that model year.
The T25 form factor of the 3057 is physically larger than the T15 of the 921, which further reinforces that the two bulbs occupy distinct housing sockets and are not cross-compatible by size alone.
The 921 bulb's 16-watt output is consistent with a dedicated single-function reverse light, where only one brightness level is required. The 3057's dual-filament design, by contrast, supports two distinct brightness levels within a single bulb.