TL;DR: The Quick Answer
- H4 bulbs are dual-beam: One bulb does both low and high beams.
- H7 bulbs are single-beam: Your car uses separate H7 bulbs for low beam and high beam.
- They are NOT interchangeable. They have different plugs and connectors.
- To know which one you need: Check your car’s owner’s manual or use an online bulb lookup tool with your vehicle’s make, model, and year. This is the only way to be sure.
You’re replacing your headlight bulb, and you’ve hit a common roadblock: Do I need an H4 or an H7 bulb? It’s a crucial question. Picking the wrong one means a wasted trip to the auto parts store and a headlight that simply won’t fit.
Don’t worry, you’re not alone. While they look similar, H4 and H7 bulbs are fundamentally different. This guide will cut through the confusion, explaining the key differences in plain English so you can buy the right bulb with confidence.
The Quick Answer: What’s the Main Difference?
The single most important difference is the number of filaments:
- H4 Bulbs: Have two filaments (low beam and high beam) in one bulb. They are a dual-beam bulb.
- H7 Bulbs: Have one filament. They are a single-beam bulb. This means your car will use separate H7 bulbs for low beam and high beam.
Think of it like this: an H4 bulb is an all-in-one solution, while H7 bulbs are specialized components used in pairs.
H4 vs. H7: A Detailed Comparison Table
| Feature | H4 Bulb | H7 Bulb |
|---|---|---|
| Beam Type | Dual-Beam (Low & High) | Single-Beam (Low or High) |
| Number of Filaments | Two (2) | One (1) |
| Bulbs Per Headlight | One | Typically two (one for low, one for high) |
| Connector Pins | Three (3) | Two (2) |
| Common Use | Older and more basic headlight systems; often found in motorcycles and older cars. | Modern headlight systems; the most common bulb type in today’s cars. |
| Performance | Good all-rounder, but each filament can’t be optimized as perfectly as a dedicated single-beam bulb. | Often provides better, more focused light output because each bulb is designed for a single purpose. |
Diving Deeper: How to Tell Which Bulb Your Car Uses
You can’t tell an H4 from an H7 just by looking at the bulb from outside the headlight housing. The connector on the back is the giveaway. Here’s how to be 100% sure.
1. Check Your Vehicle’s Owner’s Manual
This is the easiest and most reliable method. Look in the index for “headlight bulb” or “replacement bulbs.” It will list the exact bulb type (e.g., H4, H7, H11) for each light position.
2. Look Up Your Car Online
Use an online bulb lookup tool. Reputable auto parts stores like Sylvania, Philips, or AutoZone have databases where you enter your car’s year, make, and model. It will instantly tell you which bulbs you need.
3. Remove the Old Bulb and Inspect It (Safely!)
If you already have the old bulb out, the type is almost always stamped or molded onto the base of the bulb or the metal housing. Look for “H4” or “H7.”
Crucial Safety Tip: If you’re inspecting a bulb that was just in use, let it cool down completely to avoid burns. Also, avoid touching the glass of a new halogen bulb with your bare fingers, as skin oils can create hot spots and shorten the bulb’s life.
Can I Swap an H4 for an H7 (or Vice Versa)?
Absolutely not.
H4 and H7 bulbs have different bases and connectors. An H4 bulb has three pins, while an H7 has two. They are physically incompatible. Trying to force the wrong bulb into the headlight socket can damage the connector, the bulb, or the headlight assembly itself.
More importantly, using the wrong bulb type will result in incorrect light patterns. This can be extremely dangerous, as it will either blind oncoming drivers (if the low beam is misaligned) or fail to illuminate the road properly for you.