Signal Beam vs Double Beam: How to Easily Distinguish them?

When buying headlight bulbs, you may frequently see the words “single beam” or “double beam”, these are two types of LED headlights, because some automotive lighting systems are quite different from car to car, therefore, understanding your headlight system is crucial to buying the right bulbs.


Even so, some customers would still come with the questions: “what are the single beam and double beam?” “Is an H4 single or double?” “Is the headlight assembly a single beam or the bulb?” and there’s the often case that happened to some customers who bought a double beam headlight bulb for a single beam headlight housing.


In this blog, we’ll help you understand the distinction between single beam light bulbs and double beam light bulbs, and their working principle. Some frequently asked questions will also be shown at the end of the blog.

What is single beam headlight bulb?

single beam headlight introduce

(Single beam headlight bulb has one filament and emits either high beam or low beam)


Some drivers consider that single beams require a single bulb for the headlight assembly. However, it’s quite the opposite.


What you need to know is that single beams or double beams are calling attention to know how many filaments are inside the light bulb, not the headlights.


Single beam bulbs such as 9005 and 9006 only have one filament which means that it only emits one beam of light once.


The single beam headlight bulb has a single function, one bulb tends to create only one beam, either low beam or high beam separately. Therefore, you’ll need two single beam LED headlights for high beam and low beam replacement if you want to replace both. For example, the H1 bulb is for high beam and the H7 bulb is for low beam.


When the headlights are turned on, one of the headlight bulbs lights up while the other goes out, when you switch from low to high, the low beam turns down and the high beam turns on.


Each headlight assembly has its own specific bulb size and headlight system, if you install a dual beam light bulb for a single headlight assembly, it simply won’t work and will damage your headlight bulbs.


Single Beam Headlights Assembly 

 single beam headlight


Here is the single beam headlight assembly, which contains a projector and reflector, and the projector is for low beam while the reflector is for high beam. As we mentioned above, if you want to replace both low beam and high beam, you need two single beam headlight bulbs for replacement.


What is dual beam headlight bulb?


The name of “dual beam” is often misleading some drivers and making them believe that dual beam means two headlight bulbs. But as explained from the chart, dual beam systems require one bulb for both high beam and low beam.


A dual beam headlight has dual functions: there are two filaments in one bulb, one produces low beam and the other filament emits high beam.


A dual beam light bulb such as H4 and H13 can switch from low to high beam in one headlight bulb and back again. When the headlight is working, the bulb is also turning on accordingly.


Dual Beam headlight assembly

If you were to upgrade your dual beam headlight bulb into the headlight housing, you are going to see there’s a big reflector rather than two. Inside the single reflector, there will be a bulb with two filaments. Drivers who have dual beam headlight systems will only need to buy a set of headlight bulbs to replace (or upgrade) both high beam and low beam.


High Beam vs Low Beam

High beam and low beam are also relevant to the topic of single beam and dual beam headlights.


Both high beam and low beam are required by law and transportation regulators across the world. As mentioned earlier, single beam headlights produce high beam and low beam with a separate bulb, the dual beam headlights, however produce both beams with one single bulb.


To get more tips on this topic, you can visit our previous blog high beam vs low beam when should we use it when driving?


Frequently Asked Questions (FAQ)

💬Is an H4 bulb single or dual beam?

Dual beam, we can see there are two filaments in the H4 light bulb to produce high beam and low beam --- dual functions.


💬Is 9005 bulb single or dual beam?

9005 is a single beam headlight bulb, and it’s one of the most popular bulb size.


💬What happened if I install single beam headlight bulb in the dual beam headlight housing?

Using a single headlight bulb for a dual beam headlight system will not work, even if you choose the right bulb size. Dual beam headlight bulb must install in the dual beam headlight system.


💬Do I need a dual beam LED if I have dual beam halogen?

Yes, no matter your car requires a single beam or dual beam headlight bulb, it depends on your car headlight system, not the light bulb technology.


If you decide to upgrade your halogen to LED headlight, all you need to do is to choose the exact same bulb size.


💬Is the headlight dual beam or the bulb dual beam?

In general, dual beam refer to how many filaments in a bulb. Dual beam light bulb has two filaments to emit either high beam or low beam. Therefore, whether dual beam or single beam, they are related to the light bulb.


💬How do I know If I have a single beam or dual beam headlight system in my car?

You can open your headlight housing to see whether they have one or two bulbs. If there’s only one bulb, you have dual beam system, if you see two headlight bulbs, you have single beam system. You can also use some Vehicle Finder tool.


💬Is high beam and low beam the same bulbs?

Not always, as single beam headlight system has two light bulbs, one is for high beam and the other is for low beam, such as H1 is for high beam and H7 is for low beam , they are different bulbs.


If your vehicle is dual beam headlight system, it has one bulb in the headlight housing and produce high beam and low beam. In this case, the high beam and low beam are from the same bulb.

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