Lexus RX350 Dome Light Bulb Size

Additional Notes

• The Lexus RX350 dome light draws from three distinct bulb types across the 2007-2016 model years: the 12961, the DE3423, and the 578.
• The 12961 is a Philips part number designating a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. The wedge base design means the bulb is held in place by tension from the socket rather than by a separate locking mechanism.
• The DE3423 and 578 are both ANSI-standard festoon bulbs with a 41mm length and end-cap contacts, operating at 12V. End-cap contacts mean the bulb makes electrical contact at both of its flat ends rather than through a pin or wedge base.
• The 578 carries a 12W power rating, while the DE3423 listing in the specifications does not include a wattage value. These two festoon bulbs share the same physical 41mm length and contact style, which can create a risk of substitution despite the wattage difference.
• The Lexus RX350 uses the 12961 wedge bulb for the dome light across the 2010-2016 model years, with the single exception of the 2012 model year, which uses the DE3423 festoon bulb instead.
• The 2007-2009 RX350 uses the 578 festoon bulb for the dome light, making it physically and electrically distinct from the wedge-socket configuration found in most later model years.
• Because the 12961 uses a wedge base and the DE3423 uses end-cap contacts, these two bulb types are not interchangeable despite both appearing in closely adjacent model years of the same vehicle.
• The 578 and DE3423 share the same 41mm festoon form factor and end-cap contact style, meaning they are physically compatible with the same socket type, though their wattage ratings differ.