Collection: Festoon & C5W (10x31, 10x36, 10x42...)

Festoon, C5W, SV8.5: three names for the same family

As with the W5W/T10, this family of bulbs circulates under three parallel designations that mean the same thing:

• "Festoon" is the common English name, referring to the oblong (elongated oval) shape of the bulb.
• C5W is the CEE electrical designation: C for Festoon (the cylindrical base at both ends), 5 for the wattage, W for the tungsten filament. The C10W is the 10W version.
• SV8.5 is the technical designation of the base: S for the contact shape, V for Vitre (glass), 8.5 for the contact diameter in mm.

On the packaging, you will often find "Festoon C5W SV8.5" — it's the same bulb.

Finding the right festoon bulb size

The length of the festoon bulb is the critical data for a successful replacement. Three formats coexist in modern vehicles:

• 10×31 mm — the shortest. Common in city cars (compact dome light, glove box light).
• 10×36 mm — intermediate size, the most versatile. Dome light in most French and European sedans.
• 10×42 mm — the longest. Dome light in SUVs, premium sedans, and some German vehicles.

To identify your format: remove the old bulb (by gently uncliping it) and measure its total length with calipers or a ruler. The exact length is inscribed on some bulbs (e.g., "10×36").

Uses of festoon bulbs

Festoon bulbs are mainly used for front and rear dome lights (reading, ambient), trunk lighting, door lighting (on the ground and in the handle), vanity mirrors, and some technical lighting (engine compartment, interior fuse box). In short: all interior lighting that does not require high light output.

LED festoon bulbs: direct replacement

LED festoon bulbs are installed as a direct replacement for their halogen equivalent, without modification. Pure white light (4,000 to 6,500 K) more pleasant for reading, multiplied lifespan, negligible consumption. One precaution: check the exact length before purchase — a 10×42 LED festoon bulb will not fit into a 10×31 holder designed for a short festoon bulb.