194 vs 168 (T10) bulbs
The small wedge bulbs in parking lights, license plates, side markers and interiors
A T10 bulb is a small glass wedge bulb about 10 mm across, used in parking, license-plate, side-marker and interior lights. The common types, the 194, 168, 2825 and European W5W, share the W2.1×9.5d base and fit the same sockets, but differ in power, from about 3.8 W to 5 W.
Most cars carry a dozen or more of these little bulbs, in places owners rarely look: behind the license plate, in the side markers, the glovebox and the trunk. They are cheap and they all fit the same sockets, and that is the catch: a brighter bulb that fits is not always the right one.
What is the difference between 194 and 168?
Only the power. Both are T10 wedge bulbs on the same W2.1×9.5d base and fit the same sockets. A 194 draws 0.27 A at 14 V, about 3.8 W; a 168 draws 0.35 A, about 4.9 W, and is brighter and hotter. The 2825 and the European W5W are 5 W versions of the same bulb.
The 168 is the usual brighter swap for a 194, but its extra watt of heat matters in small plastic housings and behind dashboards. Where the maker specifies a 194, the cooler bulb is the safer choice. The W16W, sold in North America as the 921, is a larger bulb on the same base for reversing and third brake lights; it fits the same sockets only where the lamp has room for it.
| Bulb | Base | Power | Typical use |
|---|---|---|---|
| 194 | W2.1×9.5d | 3.8 W (0.27 A at 14 V) | Side markers, instrument and interior lights |
| 168 | W2.1×9.5d | 4.9 W (0.35 A at 14 V) | Parking, license-plate and marker lights |
| 2825 | W2.1×9.5d | 5 W | Parking and license-plate lights |
| W5W | W2.1×9.5d | 5 W, 50 lm | Position and license-plate lights in Europe |
| W16W (921) | W2.1×9.5d | 16 W | Reversing and third brake lights |
| C5W festoon | Caps at both ends | 5 W | Dome, mirror and license-plate lights |
What does T10 mean?
T10 is aftermarket shorthand for a tubular bulb about 10 mm across. US catalogs call the same size T-3¼: T for tubular, then the diameter in eighths of an inch, and 3¼ eighths is about 10 mm. T10 describes the size and base, not the power: 194, 168, 2825 and W5W are all T10 bulbs.
The same naming shows up on bigger bulbs: the 7443 is often sold as a T20 and the 3157 as a T25, roughly their glass diameters in millimeters. That is why a T-number alone cannot identify a bulb; the bulb number or European name can (see 3157 vs 7443).
Festoon bulbs
Festoon bulbs are small tubes with a pointed metal cap at each end, held between two spring clips. They light dome lights, vanity mirrors and license plates. Sizes go by length from tip to tip, commonly 31, 36, 39 or 41 mm, and European C5W and C10W festoons are 5 W and 10 W. Measure before buying.
A bulb that is too short will not reach both clips; one that is too long bends the clips, which then lose their grip. LED festoons carry their LEDs on a flat board, so check which way the board faces and that the lens still fits over it.
Choosing LED T10 bulbs
LED T10 bulbs are among the easiest car upgrades, but check four things: the LEDs must face where the filament's light went, side markers need the right color, some cars report a fault on monitored circuits, and LEDs are polarized, so if one stays dark, turn it around in the socket.
In the United States, front side markers must show amber and rear ones red, so a white LED behind a clear marker lens is the wrong color. Cars that monitor their parking and plate lamps can flag an LED bulb as failed or make it flicker; CANbus-ready T10 bulbs are built for them (see CANbus LED bulbs and hyperflash). In UNECE countries, W5W/LED and C5W/LED are approved LED substitute categories, legal in the vehicles each bulb's maker lists.
Frequently asked questions
Can I use a 168 instead of a 194?
Yes, it fits and lights, but it draws about 30% more power and runs hotter. In small plastic housings or dashboards, stick with the 194 if that is what the maker specifies.
Is a W5W the same as a 194?
Same base and size, different power: a W5W is 5 W, a 194 about 3.8 W. They interchange physically, and the W5W is a little brighter.
Why does my LED T10 bulb not light?
LEDs pass current only one way. Pull the bulb out, turn it 180° and refit it. If it still stays dark, clean the socket contacts, or check whether the car is cutting power to a lamp it sees as faulty.
What is a 2825 bulb?
A 5 W T10 wedge bulb, similar to the European W5W, used where a brighter bulb than a 194 or 168 is wanted.
Sources and further reading
- IEC 60061-1, Lamp caps and holders together with gauges for the control of interchangeability and safety: Lamp caps (W2.1×9.5d cap).
- UN Regulation No. 37, uniform provisions for filament light sources in approved vehicle lamps, with category sheets in the Consolidated Resolution R.E.5 (W5W, W16W and C5W).
- UN Regulation No. 128, LED light sources, and R.E.5 Group 4, LED substitute light source categories (W5W/LED, C5W/LED).
- FMVSS No. 108, 49 CFR 571.108: side marker lamp colors.
- Manufacturers' miniature lamp data for the 194 and 168, rated at 14 V; Narva automotive lamp catalog for festoon lengths.
Image credits
- W5W bulb: btr, CC BY-SA 2.5, via Wikimedia Commons.