What is D-homologation

A ‘D’ marking on vehicle lighting indicates that a single light may be used in conjunction with a second light to form a single approved light function. Within the type approval, the two lights therefore together constitute a single light, for example for the rear light or brake light.

D-homologation is particularly relevant for modular rear light assemblies on trucks, trailers and other commercial vehicles. However, the approval is not a general authorisation to fit three, four or more lights for the same function. The complete installation must always comply with the requirements of ECE R48 regarding the number of lights, mounting positions and visibility.

What exactly does D-homologation mean?

The D-marking is used when two separate lights are approved jointly as a single light. Each light constitutes an independent unit, but the two lights are assessed together for the same light function.

This may be relevant, for example, when two separate rear light or brake light modules are fitted on either side of a vehicle. Without the correct D-marking, two separate lights cannot automatically be regarded as a single approved light.

Whether multiple lights are actually permitted also depends on:

• the relevant light function;
• the vehicle category;
• the prescribed number of lights;
• the mounting position and spacing between units;
• the angles of visibility and light output;
• the conditions specified in the light’s type approval.

When do you need a D-marking?

A D-marking is relevant when you wish to use two separately approved lights together as a single light for the same light function. Consider, for example, two separate brake lights that together form a single approved brake light function.

Do you use different lights alongside one another for different functions, such as an indicator, brake light, rear light and rear fog light? In that case, there is no duplication of the same function. Each light must, in that instance, be individually approved for the function it performs.

Furthermore, the D-marking does not in itself determine how many lights you are permitted to fit to a vehicle. ECE R48 specifies, for each light function and vehicle category, how many lights are mandatory or permitted. A D-approval does not alter these installation regulations.

How can you recognise D-homologation?

The letter D appears in the function code of the relevant light in the official approval marking. Depending on the approved function, you may, for example, come across a designation such as:

• R1D: a rear light function suitable for use as a combination of two lights;
• S1D: a brake light function suitable for use as a combination of two lights;
• R1D-S1D: a combined rear light and brake light function, with both functions approved for this application.

The exact combination of letters and numbers may vary depending on the product and light function. You should therefore always check the marking on the lens or housing and consult the manufacturer’s datasheet or type-approval document.

Is an E-mark the same as D-homologation?

No. An ‘E’ mark indicates that a product has been approved in accordance with a specific UNECE regulation. The letter ‘D’ is an additional designation for a specific light function and indicates that the light is suitable for functioning as a single unit in conjunction with a second light.

An ECE R10 approval is also a different matter. ECE R10 relates to electromagnetic compatibility and says nothing about whether two lights may be used together as a single light function.

Do both lights require a D-marking?

When two separate lights are used together as a single approved light, the lights used must, according to their type approval, be suitable for this configuration. A D-mark on just one of the lights is therefore not sufficient.

Please use the prescribed combination of lights where possible and always follow the manufacturer’s mounting instructions. A D-marking does not mean that different light models may be combined without further verification.

Multifunctional rear lights and D-homologation

A multifunctional rear light may incorporate several functions, such as a tail light, brake light, indicator and rear fog light. Approval must therefore be assessed for each individual light function. Consequently, a light unit may have a D-marking for one function but not for another.

If a lighting unit consists of several modules that have been approved by the manufacturer as a single complete system, the system may be regarded as a single light within the type approval. This is different from combining individual lights yourself. Connecting individual modules without the corresponding type approval does not automatically comply with the regulations.

Frequently asked questions about D-homologation

Does D-homologation mean you can fit an unlimited number of lights?

No. The D marking refers to a set of two lights. The permitted number of lights is determined by the installation regulations of ECE R48 and may vary depending on the light functions and vehicle category.

Are you allowed to combine two different lights with a D-marking?

Not automatically. The lights must be suitable for use together in accordance with their type approval and the manufacturer’s instructions. The presence of a D-mark alone does not prove that any random light model may be combined with another model.

Is D-homologation the same as dual homologation?

The term ‘dual homologation’ is used in practice for lamps which, as a combination of two lamps, are permitted to fulfil a single light function. The technically more precise term is a D-marking or approval for a combination of two lamps.