9003 vs H4 Headlight Bulbs | What’s the difference?

In this article, we’ll be outlining the main differences between 9003 and H4 headlight bulbs.

Many people believe that these two bulbs are exactly the same, however there are some slight differences in compatibility and use case.

Specifically, there is a difference in the shape of the base of each bulb. There are also certain differences that make one legal for on road use and the other illegal.

Other than these few differences, these two bulbs are largely the same. We will go into deeper detail below.

I have over a decade of experience working on cars and headlights, allowing me to have a better understanding of the differences between 9003 and H4 bulbs.

Keep reading for more information on the differences between 9003 and H4 bulbs.

Meant for use on road carsOriginally used on race cars and motorcycles
Double filament with less brightnessDouble filament with higher output
Does not dazzle other driversDistracts oncoming traffic
Will not fit in an H4 housingWill fit in 9003 housing
Less tolerant of vibrationsMore tolerant to vibrations
Usually seen on American vehiclesMore common on European models
Three pronged baseL-shaped base
Completely legal for on-road useCannot legally be used in place of 9003 bulbs
9003 vs H4 Headlight Bulbs



To fully understand the differences between these two bulbs, we have to understand where they came from. 9003 bulbs were initially designed to be used on American model cars. H4 bulbs on the other hand, were mostly found on European model race cars.

Moreover, H4 bulbs, when they were first introduced into the American market, we’re only used on motorcycles. Only later, did people start using them on cars and trucks.


Another noticeable difference is in the brightness of these two bulbs. H4 bulbs are slightly brighter and have a higher output of light. While both 9003 and H4 are double filament bulbs, 9003 produces less lumens.

Power consumption

Because of the higher output, H4 bulbs usually draw a little bit more power than their 9003 counterparts. However the difference is nominal and does not result in any appreciable energy savings.

Socket shape

One of the easiest ways to tell apart H4 and 9003 bulbs is the shape of their sockets. 9003 bulbs have a three pronged base with equal sized tabs. H4 bulbs on the other hand, have an L-shaped base and the bottom tab is slightly shorter than the rest.


It is a common misconception that 9003 and H4 bulbs can be used interchangeably. The fact is that because of the different shapes of their bases, it is impossible for a 9003 bulb to fit in an H4 housing. However, an H4 bulb will fit in a 9003 housing.


One of the perceived benefits of using H4 bulbs in place of 9003 bulbs is that because they were designed for use on motorcycles, they can withstand greater vibration and are more durable. However there is only anecdotal proof to support this claim and it should not influence your buying decision.


As mentioned before, H4 bulbs were originally fitted to European race cars and in other markets, they are only intended to be used on off-road vehicles. This is because they have significantly higher light output which can dazzle oncoming traffic, making them unsafe for road use. As such it is illegal to use H4 bulbs in place of 9003 bulbs on roads and highways.


So to sum up, 9003 and H4 bulbs may look and perform similarly, however each has different use cases.

9003 bulbs are for on road use, whereas H4 bulbs are not road legal as they can be a safety hazard for oncoming traffic. H4 bulbs can be fitted into 9003 sockets, but not the other way around.

Another important distinction is that H4 bulbs are commonly seen on motorcycles and off road vehicles. And H4 bulbs are believed to be more tolerant to vibrations.

So really, each bulb caters to a different need and use case. Whichever bulb you decide to buy, we have tested the vast majority of available options and reviewed the top performers. Find out more about 9003 and H4 bulbs in other articles on our site.

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Hi, I'm Graeme, the author and owner of HeadlightReviews.com. Before I started this hobby site, I used to work alongside my 'Pops', helping out as he worked as a mechanic for over 50 years. Twenty-five of those he was running his own Auto Electrician & Body Shop, where I fell in love with vehicle lighting. I've taken all our experience online (that's not his gig)… so it’s safe to say there are very few people on the internet who can match our expertise and deep understanding of vehicle mechanics, repairs, parts, and especially headlights. If you've got a bulb question, contact me here, and read more about me and headlightreviews.com here.

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