W5W / T10 Bulb
Light Bulbs & Sockets · 7 specs
Direct Answer
The W5W Bulb (commonly called a T10 Wedge or 194 / 168 in North America, standardized under ECE Regulation 37 with a W2.1×9.5d base) is the universal automotive miniature capless glass bulb. Operating at 5W at 12V (generating ~50 lumens), it is the standard for front parking lights, side turn indicators, license plate lamps, and cabin interior courtesy lights.
Source: UN ECE Regulation 37 Category W5W / US DOT 194/168 Standards / IEC 60061-1 (7004-21) · Last reviewed Aug 28, 2026
Specs
| Standardization | UN ECE R37 Category W5W / US DOT Type 194 / 168 / IEC 60061-1 |
| Base Socket Designation | W2.1×9.5d (Capless glass wedge base: 2.1 mm thickness × 9.5 mm width) |
| Bulb Envelope Diameter | T10 designation indicates tubular glass envelope diameter of 10.0 mm (3/8 in) |
| Nominal Power & Voltage | 5 W @ 12V (tested at 13.5 V; draws approx. 0.40 A) |
| Luminous Flux Output | 50 lumens ± 20% (at 13.5 V) |
| Electrical Contact Wires | Two bare molybdenum lead wires folded across opposite sides of the flattened glass wedge base |
| Applications | Front sidelights/eyebrow markers, side fender repeaters, license plate illumination, interior map/dome lights, trunk cargo lamps |
The Capless Wedge Design
Unlike brass bayonet bulbs that require a metal base sleeve and solder contacts, the W5W / T10 wedge is completely capless: the glass envelope itself is pressed flat at the bottom during manufacturing, and the internal molybdenum filament leads are simply bent over the glass tab. It pushes directly into a spring-tensioned plastic socket, resisting corrosion and road vibration.