Lexus IS350 front side marker bulbs use 12961 or 194 size, while rear side marker bulbs use 194 size. The replacement bulb chart covers 2006 through 2019 production years.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 194 bulb is the most frequently specified size across the Lexus IS350 side marker positions, covering both front and rear applications for the 2006-2009 model years.
The 194 is an ANSI-standardized miniature wedge bulb of the T10 type, rated at 12V and 3.78W, recognized across the United States and Canada.
The 12961 is a Philips part number designation for a T10 miniature wedge bulb fitted with a W2.1x9.5d base, rated at 12V and 5W.
The Lexus IS350 (2019) front side marker uses the 12961 bulb, which draws more wattage than the 194 at 5W versus 3.78W.
Both the 194 and 12961 share the T10 wedge form factor, though the 12961 carries a specific W2.1x9.5d base designation that reflects a standardized IEC base classification.
Despite the shared T10 form factor, the wattage difference between the 194 and 12961 means the two types are not confirmed interchangeable across model years in these specifications.
The rear side marker position on the IS350 is only specified for the 2006-2009 model years, exclusively using the 194 bulb.
The W2.1x9.5d base notation on the 12961 describes the wedge contact width in millimeters and the pin spacing, which is a standard IEC 60061 base code used for miniature wedge lamps.