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Automotive lighting systems differ from car to car and can easily get confusing for those not very familiar with cars in general or car lighting more specifically.
Whether you're looking to replace halogen bulbs or to upgrade LED or HID headlight bulbs using an aftermarket conversion kit, understanding your car's lighting system is critical to purchasing the right bulbs.
The most frequent issue we see on a daily basis is customers trying to buy dual beam bulbs for a single beam headlight system in order to save a few bucks. As we'll explain in this guide, this doesn't work and will end up wasting your time and money.
In this guide, we'll explorethe differences between a single beam and dual beam headlight systems and bulbs, how they work and conclude with some questions we frequently receive from our customers on this subject.
Most of the confusion surrounding headlights is the difference between single beam bulbs and dual beam bulbs.
Briefly speaking, a single beam headlight system uses two headlight bulbs, one for the low beam and another for the high beam. On the other hand, a dual beam headlight system uses one bulb for both the low and high beam.
|Single Beam||Dual Beam|
|Number of bulbs||Two (2)||One (1)|
|Number of filaments||One (1)||Two (2)|
|Low beam function||Yes||Yes|
|High beam function||Yes||Yes|
|Price of bulb ($)||Lower||Higher|
|Examples||H7, H11, 9005, 9006||H4, H13, 9004, 9007|
|Impacts fog lights||No||No|
In very rare cases, dual beam headlight systems may use a single beam bulb.
The name 'single beam' often confuses drivers, leading them to believe the headlight requires a single bulb, however, it's quite the opposite. Dual beam systems require only one bulb for both beams as we explain in the next section.
Single beam headlight bulbs such as H11 and 9005 work exclusively with one beam, either the low or the high beams.
As such, single beam systems require two bulbs total, one to create a light beam for the lows and a second to create a beam for the highs. Single beam bulbs have one filament, which means it only emits one beam of light at a time.
If you try to save money by buying a dual beam bulb for your single beam headlight system, it simply will not work. Each assebmly has its own specifc bulb size and headlight mechanism.
Dual beam headlight systems work with one specialized bulb that can create two beams (low and high beams). Dual beam bulbs such as H4, H13, and 9007 have two filaments, which allows them to create two beams (high and low) when both are activated.
The name 'dual beam' is misleading as drivers often think it means the headlight system requires two bulbs but as explained, dual beam systems require one bulb for both beams.
Certain cars (albeit very few) have headlights that use single-beam bulbs in a dual-beam system. This is achieved using a shutter mechanism.
The way these assemblies work is that a shutter blocks off a section of the headlight reserved to project light upward (like a normal high beam would). When the high beam is activated, the shutter opens creating the high beam effect.
It is worth pointing out that single-beam headlights will never using dual-beam bulbs.
You may be wondering how the low beam and the high beam functions fit within the conversation of single-beam and dual-beam headlights.
Both these functions are present in both systems and are in fact required by law and transportation regulators across the world. The only difference, as already explain in this resource, is that single-beam headlights will produce each beam with a separate bulb while dual-beam bulbs will produce both beams with one single bulb.
To learn more on this topic, visit our guide on the difference between low beam and high beam headlight function.
No. Using a dual beam bulb for a single beam system will not work. A dual beam bulb will not fit and comes with 2 filaments, something your single beam headlight system is not equipped to handle. You will need two sets of the specific bulbs for your car for each of your high and low beams.
No. Using a single beam bulb for a dual beam system will not work. A single beam bulb will not fit and only has one filament, which means that your high beams would not work even if the bulb did fit. You will need one set of the specific dual beam bulbs for your car's dual beam system.
Yes. Whether your car requires a single or dual beam bulb depends on your vehicle's headlight system, not the bulb technology.
So, if your car comes equipped with dual beam bulbs, you will need to get the exact same bulb size when upgrading your lights to either LED or HID.
9005 is a single beam headlight bulb. This is one of the most popular bulb sizes.
H13 is a dual beam headlight bulb, it is one of the most popular dual beam headlight bulb sizes.
Generally, the bulb is the one that is dual beam since it's the part of the headlight system that has the function to emit two light beams. It can be argued that the headlight is also a dual beam since it only has room for one dual beam bulb.
However, for a very limited number of cars, it is the headlights that are dual beam. These headlights come with a flap function that creates two beams out of one bulb.
Fog lights always use single beam bulbs since they can only emit one light beam unlike headlights, which must emit both a high and low beam regardless of whether a single or dual beam.
Bi-xenon bulbs are dual beam bulbs where both filaments (beams) use HID/Xenon technology. This specific term exists because HID/Xenon dual beam bulbs can come in a second form, where the low beam is HID/Xenon technology and the high beam is halogen, in which case it is called a hi/low bulb.
Many people often think bi-xenon simply mean dual beam but that is not accurate. For example, asking for a bi-xenon LED bulb technically makes no sense at all.
Look at your car's headlight to see whether there are one or two bulbs. If you see two bulbs, you have a single beam system. If you only see one bulb, you have a dual beam system. Do not count the turn signal bulb should your car's headlight come with one.
Alternatively, you can use our Vehicle Finder tool. Should your car have a dual beam system, you will see one the following dual beam bulbs listed: H4 (Dual-Beam), H13 (Dual-Beam), HB2 (Dual-Beam), 9003 (Dual-Beam), 9004 (Dual-Beam), 9007 (Dual-Beam), 9008 (Dual-Beam), D1S (Dual-Beam), D2S (Dual-Beam), D2R (Dual-Beam).