H4 Bulb
Light Bulbs & Sockets · 7 specs
Direct Answer
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.
Source: UN ECE Regulation 37 Category H4 / US FMVSS 108 (HB2 / 9003) / IEC 60061-1 (7004-39) · Last reviewed Aug 28, 2026
Specs
| Standardization | UN ECE R37 (H4) / US DOT FMVSS 108 (HB2 / 9003) / IEC 60061-1 |
| Base Socket Designation | P43t (3 large radial metal locating tabs with 3 heavy electrical blade terminals) |
| 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 |
| Luminous Flux Output | Low Beam: 1,000 lumens ± 15% | High Beam: 1,650 lumens ± 15% (at 13.2 V) |
| 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 |
The Internal Anti-Glare Shield Mechanics
The ingenious design of the H4 bulb lies in its internal metal shield under the forward low-beam filament. By blocking light rays from hitting the bottom half of the headlight reflector, light only bounces off the top parabolic reflector and is angled downwards toward the road, preventing oncoming drivers from being blinded without requiring movable mechanical shutters.