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HomeFeatured ArticlesH1, H3, H4, H7, H11, HB3, HB4 | Headlight Sockets Explained

H1, H3, H4, H7, H11, HB3, HB4 | Headlight Sockets Explained

If you have scouted the market for a new aftermarket bulb for your vehicle, you must have witnessed a plethora of different bulb categories. Talking about headlights and fog lights, there are many types, H1, H3, H4, H7, H11, HB3, HB4 and more. Well, before today, did you know the difference between each bulb type and its significance? Either way, let’s have a detailed look at these different types of bulbs and light sockets and why are they like that.

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Why are the bulbs classified?

Halogen Headlight Bulb
Halogen Headlight Bulb

There are several carmakers across the globe, and these manufacturers have plenty of vehicles in their portfolio. If there were a different bulb for all the different cars, it would have been next to impossible to get a replacement or even a bulb in the aftermarket. Okay, if there was a replacement bulb by chance, it would have coasted a dime. to

Now, to standardize the bulb market, definite bulb classifications were introduced. The World Forum for Harmonization of Vehicle Regulations (ECE Regulations) develops and maintains the international standards of various automotive products; light bulbs are one of them.

Car Fog Lamps // Image for representation

To begin with, these light bulbs are classified into 3 different groups;

  • Group 1

    H7 bulb / Group 1 Bulb
    H7 bulb / Group 1 Bulb

    Most of the bulbs in a modern vehicle belong to Group 1. These include H7, H11, HB3, HB4 H1, H3, H4. This group contains headlight bulbs and takes in fog light bulbs. But of course, the sockets for the bulbs are different. Also, do note that all the bulbs in Group 1 may or may not have the same power ratings.

  • Group 2

    H6W bulb / Group 2 Bulb
    H6W bulb / Group 2 Bulb

    The other classification is Group 2. This group has many lights in its set, these include, turn indicator bulbs, tail light bulbs, registration plate bulbs and also the bulb for the cornering lights. Bulbs in Group 2 have C5W, H6W, HY6W and more.

  • Group 3

    H2 bulb / Group 3 Bulb
    H2 bulb / Group 3 Bulb

    In the end, we have group 3. The bulbs in this category are now obsolete and are not used in modern cars. Still, these include H2, C21W, P19W types of bulbs.

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For now, let’s focus on the bulbs from Group 1, as these are most likely to be replaced or upgraded.

Group 1 automotive light bulbs

Headlights | GoMechanic
Halogen Headlights

As discussed earlier, the group 1 automotive light bulbs include all conventional types like H1, H3, H4, H7, etc. These bulbs are used depending upon their use and power requirements. Group 1 bulbs are installed in headlights and foglights for the most part.

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  • Also, this means even if the power ratings are the same, you cannot interchange the bulb with a different type.
  • It has to have the same socket. That said, depending upon the bulb housing or the socket, the bulb’s filament and the coupler also varies.
  • For example, the H4 bulb has two filaments (one for high beam and the other for low beam), whereas the H7 only has one. A conventional headlight with a single reflecting surface can use an H4 bulb.
  • But if a vehicle uses H7 bulbs, it has to have a twin-pod setup, one pod for high and the other for low beam. Naturally, the light intensity and power will vary with vehicle type.

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Now, with the type clear which one to choose?

Automotive Bulb TypesAutomotive Bulb Types
Automotive Bulb Types

The simple answer, you cannot just go out and get any bulb. To know which bulb your car uses, there are two things you can do.

  1. Open up the web browser and search for it, Simple? However, there is a catch. The type of bulb mentioned at times is not correct on the internet.
  2. The safer option is to grab the owners manual and check for the details.

Pro Tip: Along with looking for the bulb type, check the power (watts) that the bulb uses. This will prevent the fuse from blowing unnecessarily.

Informative Read: LED Lights/Bulbs, Projector Vs Reflector Headlights

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Utkarsh Bhardwaj
Technical Content Strategist at GoMechanic | Big Time Petrolhead with the passion for building cars and driving those beauties.

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