Are there two bulbs in a headlight?
In many cars, headlights may use either two separate bulbs (one for low beam, one for high beam) or a single bulb that contains two filaments for both functions. The exact setup depends on the model and the technology (halogen, HID, or LED).
How headlight designs vary by technology
Headlights come in a few mainstream architectures. The choice reflects cost, packaging, and performance goals. Below is a snapshot of the most common layouts you’ll encounter on today’s vehicles.
Here are the typical configurations you’ll encounter in headlights today:
- Two separate bulbs per headlight: one dedicated to low beam and one dedicated to high beam. This design is common in older halogen systems and in many trucks and some SUVs where easy bulb replacement is a priority.
- A single dual-filament bulb per headlight: one bulb contains two filaments, enabling both high and low beams from the same unit (examples include H4 and H13 types). This is especially common in many European and Asian vehicles from the 1990s onward.
- LED- or projector-based headlights with multiple modules: modern headlights may use several LED modules or light sources within the same housing, and beam patterns are produced by the arrangement, optics, and electronics rather than by separate replaceable bulbs.
In practice, the number and type of light sources in a headlight depend on the design and the era of the vehicle. If you’re replacing a bulb, always verify the exact part number and fitment for your car.
Practical implications for owners
Two separate bulbs per headlight
Proponents say it’s straightforward to replace a single failing function (low or high beam). A drawback can be the need to stock and replace two different bulb types and wattages.
Dual-filament single bulb
With a dual-filament bulb, replacement is often simpler since you replace one bulb for both beams. However, it means a single bulb failure can dim both beam functions until replacement.
LED/module-based headlights
LED and other module-based headlights rarely use replaceable "bulbs." Instead, individual LED modules or the entire headlight assembly may be replaced. This can be more expensive but often yields longer life and advanced lighting control.
Summary
Bottom line: there isn’t a universal rule. Some headlights literally have two separate bulbs, others use a single dual-filament bulb, and many modern systems rely on LED modules rather than traditional bulbs. Always check your vehicle’s owner manual or consult a professional to identify the correct parts and replacement procedure for your specific headlight design.
