H4 Bulb vs. W5W / T10 Bulb
Comparing 2 standards across 11 specifications. 11 key differences identified.
The H4 Bulb (marketed as 9003 or HB2 in North America under DOT regulations, standardized with a P43t 3-prong base) is the legendary dual-filament automotive headlight bulb. Containing both a 55W low-beam filament (equipped with an internal stamped metal anti-glare shield cup) and a 60W high-beam filament inside a single halogen quartz glass capsule.
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.
Specification Comparison Table
11 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standardization
|
UN ECE R37 (H4) / US DOT FMVSS 108 (HB2 / 9003) / IEC 60061-1 | UN ECE R37 Category W5W / US DOT Type 194 / 168 / IEC 60061-1 |
|
Base Socket Designation
|
P43t (3 large radial metal locating tabs with 3 heavy electrical blade terminals) | W2.1×9.5d (Capless glass wedge base: 2.1 mm thickness × 9.5 mm width) |
|
Luminous Flux Output
|
Low Beam: 1,000 lumens ± 15% | High Beam: 1,650 lumens ± 15% (at 13.2 V) | 50 lumens ± 20% (at 13.5 V) |
|
Filament Architecture
|
Dual tungsten filaments: Low Beam (55W) + High Beam (60W) | — |
|
Internal Anti-Glare Shield
|
Stamped nickel cup positioned under the low-beam filament blocks downward light, creating a crisp horizontal beam cutoff | — |
|
Electrical Connector
|
3-prong female socket (Ground, Low Beam 12V+, High Beam 12V+) | — |
|
Application Domain
|
Standard in motorcycles (single headlight unit), compact hatchbacks, classic 7-inch round sealed-beam replacements | — |
|
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) |
|
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 |