What is an H4 Bulb?

For those unfamiliar with the many kinds of headlight bulbs, figuring out the difference between each bulb can be confusing. Knowing more about the differences between various automotive bulbs and fittings will help you shop for the best bulbs for your car. In this article, we’ll learn more about the H4 bulb and its uses.

Types of Bulbs

There are several main categories of bulbs found in today’s vehicles. Some bulbs can be used for major functions, such as headlights or brake lights. Other bulbs are only used for smaller parts, like interior lights or signalling lights. Drivers are usually only concerned with the first category, as these are the bulbs you’ll use to illuminate the road.

H4 bulbs fall into this first category. They are unique because H4 bulbs are only used in headlamps, thanks to some special properties we’ll discuss later in this article.   

Fittings

There are many different bulb fittings out there. If you’re shopping for headlight bulbs, you’ll likely find that the most common are H1, H3, H7, and H4, among others. What makes each bulb unique is the type of fitting or base, most easily identified by the prongs that are used to plug in the bulb.

Most headlamp bulb fittings, including the popular H1 and H7 bulbs, have two prongs on the base. Some bulbs, such as the H3 bulb, look a bit different. The H4 is easy to identify because of its three-pronged base, which is unique among these different bulbs.  

Filaments

Most headlight bulbs, including those we’ve mentioned here, are single-filament bulbs. This means there is only one filament, or wire, inside the bulb. Filaments are the part of the bulb that actually lights up, producing the glow that illuminates the road.

While H1, H3, and H7 bulbs all have just one filament, the H4 is a dual-filament bulb. Instead of only one wire producing light, the H4 bulb has two. This allows the H4 bulb to serve as both the main beam and dipped beam headlights in one single bulb. With other types of headlight bulb, you’ll need to purchase two separate bulbs—one for the main beam and one for the dipped beam.

Clearly, this makes the H4 bulb superior to most other headlight bulbs in terms of convenience. It can also save drivers time and money, as you’ll purchase fewer bulbs and save yourself the hassle of replacing both main and dipped beam bulbs. You can read more about the difference between main beam and dipped beams here.

Uses and Availability

The H4 bulb was originally invented for use in race cars. However, its use was primarily restricted to European cars for decades. In the United States, H4 bulbs were popular in motorcycles, but couldn’t be used in cars or trucks due to legal restrictions requiring sealed headlamps.

Even when these restrictions were lifted, H4 bulbs were banned by regulatory agencies in the United States. The dual-filament bulbs were not precise enough to meet restrictions on beam patterns for U.S. headlamps, as they could easily point upwards and blind oncoming traffic.

As a result, an alternative bulb called the HB2 or 9003 was developed. This can be rather confusing for consumers. The H4, HB2, and 9003 are essentially all the same bulb and can be used interchangeably. Many bulbs that fit this specification will feature all three labels on the packaging.  

Halogen v LED

H4 bulbs are available in both halogen and LED. Halogen Headlight bulbs are the traditional style of auto bulb. They are typically the least expensive type of bulb, especially when compared to newer Xenon HID bulbs. Modern halogen H4 bulbs come in a variety of styles and their performance rivals that of Xenon bulbs.

LED car headlights are often used by drivers who want a stylish look for their headlamps. They are more expensive than halogen bulbs, but last much longer. LED bulbs may have a cooler colour temperature, meaning they appear to be a bright white or blue colour.

If you want a modern look and long-lasting performance, LED bulbs are great. However, LED H4 bulbs are not legal for use on the road as headlight bulbs. For many drivers, this means halogen bulbs are your only viable option.

When to Use H4 Bulbs

Drivers don’t have much choice when it comes to the bulbs in their headlamps. Since different bulb types have different fittings, they aren’t interchangeable. If your vehicle requires H4 bulbs, you can’t simply switch to another bulb fitting. The only exception is the HB2 or 9003 bulb, which are identical to H4 bulbs.

Not sure what kind of bulbs you need? Check to find the right bulb fitting for your vehicle using the bulb finder on our home page. If your car takes H4, HB2, or 9003 bulbs, shop our selection of certified halogen bulbs for your headlamps or LED bulbs for a stylish off-road look.

Shop car headlight bulbs at PowerBulbs.