Automotive globe fittings explained
— June 06, 2021 | 2 min read
Vehicle headlight globes and their fittings are generally a set and forget kind of arrangement. Automotive manufacturers choose a headlight globe fitting and appropriate globe to meet a long list of requirements and standards, and you and I will need to work within those parameters when replacing our globes or uprating the output of light to suit our own driving needs.
But what if you’re starting from scratch…? Anyone who has built their own vehicle, caravan, boat, or truck will know there’s a wide variety of headlight globe fittings and globes available to suit a multitude of applications. Many of these are the same used as vehicle manufacturers, too.
All bases covered
Choosing the correct base is something most of us don’t have to worry about. Most modern incandescent headlights and accessory lamps have the base (also known as the cap) built in, allowing you to simply change the globe when it expires. But assuming you’re choosing a light to match the globe type fitted to your vehicle, then you’ll need to understand the common types of fittings offered to the market.
For the most part, H1, H3, H4, H7, H11, HB3, and HB4 classifications are the common base selections shared between vehicle headlights and accessory lamps. If you’re unsure which type your car has, you can consult your owner’s manual, or remove the globe and check the stamping on its metal base. The alpha-numeric code will then tell you if the globe is compatible with that you might plan on using in your accessory lamp and allow you to shop for a match accordingly.
We just spoke about incandescent headlight globe classifications as they relate to the base or socket of the headlight globe. This classification also applies to the globe itself as the electrical connector and ultimately globe type must fit the same pattern as the socket they attach to.
H type globes, for example, are in the Group 1 classification. This standard is determined by the United Nations who have set international standard (UN Regulation 37) for classifying vehicular globes to ensure consistency across different countries. Importantly, these classifications also govern the approval process used for national testing bodies and their subsequent gradings, including ECE or Economic Commission for Europe and ADR or Australian Design Regulations. We’ll look at more classifications in a moment.
And while many globes may look the same, and indeed offer the operate on the same voltage and produce the same light output, only a globe of a particular type will fit its matching socket. That is, they are not interchangeable. This applies not only to headlight and accessory lamps, but also park light globes, indicator globes, brake and tail-light globes, instrument panel globes, and so on.
Group 1 – lights used to illuminate the road (i.e.: headlight globes, driving light globes, fog lights).
Group 2 – signalling and marker lights (i.e.: cornering globes, reversing lights, numberplate lights).
Group 3 – older vehicle lights (i.e.: no longer standard fitment, manufactured as replacement only).
Incandescent headlight globes use a conducting wire or thread with a high melting point known as a filament which is heated by electrical current to produce light. The filament looks like a fine wire supported by two rigid wires and is often made of tungsten and is often coiled to produce more light.
In some instances, you may notice more than one filament within the globe. This is typical where globes serve multiple functions, such as low and high-beam headlight globes (e.g.: H4) or park and brake-light globes (e.g.: P21/5W), where one filament serves each purpose. The other H series globes we listed above (H1, H3, H7, H11, HB3 and HB4) are all single filament globes.
Broadly speaking, the fittings listed above all produce the same volume of light, but the voltage they require to operate (in most instances 12 or 24) and the wattage they produce – also known as nominal power – is different for each globe. To make things even more complicated, most of these globes are available with different nominal power ratings.
Because each globe requires and outputs a slightly different amount of ‘power’, it’s dangerous to interchange one bulb with another. Think of it like trying to plug an American or European appliance into an Australian wall outlet. In this case, and in the ‘base’ scenario of our automotive headlight globes, a different socket should prevent any confusion.
Finally, it’s worth noting that problems will mostly occur when switching between fittings. If you’re looking to upgrade your vehicle’s headlight globes, you shouldn’t have any problems with wattage or voltage changes unless you’re installing an aftermarket kit. Performance globes are generally a better option and will work with your vehicle’s electric system to ensure the correct current is drawn.
And don’t forget, if you’re ever unsure of what globe is the correct fit for your vehicle’s application, you can always check the Narva Globe Application Guide, your vehicle owner’s manual, or consult your local automotive parts professional.