CISPR 25 Classes 1 to 5: What does this EMC standard mean for vehicle lighting?

Electronics on board a truck or semi-trailer must be able to operate without interference. However, LED lighting with switching drivers can cause electromagnetic interference that affects radio, DAB, GPS or communication systems. CISPR 25 is the international measurement standard used to measure and limit electromagnetic emissions in order to protect on-board receivers. Class 5 is the most stringent class, but it is not automatically mandatory. This article explains what CISPR 25 means for vehicle lighting, what classes are available and how to choose the right one.

In this blog you will read:

• What CISPR 25 measures and why;
• Why LED lighting can cause interference;
• the five classes defined by CISPR 25;
• Which class is right for your vehicle?;
• The difference between ECE R10 and how to verify an EMC claim.

What is CISPR 25 in relation to vehicle lighting?

CISPR 25 is a technical measurement standard for electromagnetic emissions from vehicles and vehicle components. In the case of vehicle lighting, the light is tested as a component or electronic sub-assembly. The current edition is CISPR 25:2021, with a total measurement range of 150 kHz to 5,925 MHz.

The aim is clear: to protect on-board receivers from interference caused by components within the same vehicle. Examples include radios, DAB, GPS/GNSS and communication equipment. The standard therefore does not assess the light output of a lamp, but rather the electromagnetic emissions that may interfere with on-board receivers.

TRALERT® supplies LED vehicle lighting that has been tested in accordance with international EMC standards. You can see straight away in the TRALERT® lighting shop which products comply with these standards.

Why can LED lighting cause EMC interference?

Modern LED lighting uses electronic drivers that rapidly switch the voltage. Pulse-width modulation for dimming also causes rapid current fluctuations. These switching frequencies can generate electromagnetic emissions. These then propagate via the cabling or radiate as an electromagnetic field. Without proper EMC interference suppression, this can interfere with the operation of sensitive equipment.

What is tested?

CISPR 25 distinguishes between two types of emissions. It is useful to understand this distinction, as it determines the source of any interference.

Conducted emissions are interference that propagates via the light’s power and signal cables. Radiated emissions leave the component as an electromagnetic field and thus affect other systems. For a vehicle manufacturer, this distinction is more important than the exact measurement setup: the difference between interference via the cabling and interference via radiation determines the approach.

What CISPR 25 classes are there?

CISPR 25 has five limit classes, ranging from Class 1 to Class 5. Class 1 has the most lenient emission limits. Each subsequent class applies stricter limits, with Class 5 being the strictest. The standard does not generally specify which class a vehicle lamp must meet.

Class	Relative stringency	Practical guidance
Class 1	Lowest	Widest permitted emission limits
Class 2	Limited	Stricter than Class 1
Class 3	On average	Mid-range between the most generous and the strictest limits
Class 4	High	Stricter control of emissions
Class 5	Highest	The strictest limits within CISPR 25

The terms ‘lowest’ and ‘highest’ here refer only to the stringency of the emission limits, not to the product quality or suitability of a light.

Which CISPR 25 class do you need?

The correct class does not depend on a single fixed rule, but on the vehicle’s configuration. Consider the following factors:

• the requirements of the vehicle manufacturer or OEM;
• the position of the lighting in relation to aerials;
• the radio, DAB, GPS/GNSS and communication systems on board;
• the type of vehicle and the application;
• the consequences of potential communication faults;
• the results and scope of the truck report.

There is therefore no general rule stating that every truck requires Class 3 or every emergency service vehicle requires Class 5. The required class is determined by the OEM specifications and the EMC risk analysis of the vehicle configuration.

Vehicle manufacturers consider not only the specified class, but also the mounting position, cable routing and distance from antennas. Particularly in vehicles with multiple communication and navigation systems, the lighting is taken into account as part of the overall vehicle configuration.

What is the difference between CISPR 25 Class 3 and Class 5?

Class 3 and Class 5 are two classes that feature in product specifications. The difference lies in the stringency of the emission limits. Class 5 sets stricter emission limits than Class 3. This class may therefore be relevant for sensitive recipients or where there are strict OEM requirements, provided the truck results cover the relevant measurement methods and frequency ranges. However, a higher class is not necessarily better for every application. The decisive factor is whether the class meets the requirements of your vehicle configuration.

Practical benefit: A CISPR 25 result is only valid under the tested conditions, such as voltage, operating mode and cable length. The same light may behave differently in a different installation scenario. You should therefore check for which measurement method and frequency ranges the specified class has been achieved, and ask for the truck report rather than just the class rating.

CISPR 25 versus ECE R10

CISPR 25 and ECE R10 appear similar, but regulate slightly different aspects. This distinction is important when assessing a lighting product.

Aspect	ECE R10	CISPR 25
Character	Type-approval regulations for EMC	Technical measurement standard
Range	Vehicle and electronic sub-assemblies	Vehicles and components/modules
Objective	EMC type approval of vehicles and electronic sub-assemblies	Protection of on-board receivers

In short, ECE R10 governs the EMC type approval of vehicles and electronic sub-assemblies. CISPR 25 sets out measurement methods and limits specifically aimed at protecting on-board receivers. The documents may be relevant in parallel, but are not interchangeable.

How do you verify an EMC claim?

A strong EMC claim must be verifiable. You should therefore prefer wording such as ‘tested in accordance with CISPR 25’ or ‘complies with Class 5 limits’, supported by a truck report. The term ‘CISPR 25-certified’ on its own means little without a report. If in doubt, ask which edition of CISPR 25 was applied and exactly which emission tests – conducted or radiated – the claim covers.

What if interference does occur?

Even approved lighting can cause interference in a specific installation. An ECE R10 approval reduces the risk, but does not guarantee interference-free operation in every vehicle configuration. If you experience radio interference when switching on the lighting, the diagnosis should start with the installation itself. For more general issues, our guide to troubleshooting faults caused by LED lighting will help you further.

CISPR 25 lighting from TRALERT®

TRALERT® develops LED vehicle lighting with a focus on reliable operation, even on EMC-sensitive vehicles. If you would like to know whether a specific product complies with a particular CISPR 25 class, and which edition and truck methods the truck result covers, please consult the product specification or put your question to our team.

Are you unsure which CISPR 25 class suits your vehicle configuration? Browse our range of LED lighting for trucks or discuss your situation with our specialists. This will help you choose lighting that meets the requirements of your vehicle and the sensitivity of the on-board equipment.

Frequently asked questions about CISPR 25

Is CISPR 25 Class 5 mandatory?

No. Class 5 is the strictest emission class within CISPR 25, but the standard does not stipulate that every vehicle lamp must meet this class. The required class is determined by the vehicle manufacturer’s or OEM’s specifications and by the EMC risk analysis of the vehicle configuration, not by a general rule.

Is ECE R10 the same as CISPR 25?

No. ECE R10 is a type-approval regulation for the electromagnetic compatibility of vehicles and electronic sub-assemblies. CISPR 25 is a technical measurement standard that focuses on emissions which may interfere with on-board receivers. They complement each other, but are not interchangeable and serve different purposes.

Can ECE R10-approved lighting still cause radio interference?

Yes, that is possible. An ECE R10 approval reduces the risk of interference, but does not provide a warranty for compatibility with every vehicle installation. Factors such as cabling, mounting position and proximity to antennas influence the final result. In the event of interference, further diagnosis of the installation is required to identify the cause.

How can you recognise CISPR 25-tested lighting?

Regarding the truck report. A reliable claim specifies the edition of CISPR 25 applied, the class achieved and which emission tests were carried out. The wording ‘tested in accordance with CISPR 25’ or ‘complies with the limits of Class 5’ is more precise than the vague term ‘certified’. You should therefore always ask for the underlying report.

Sources

• IEC, CISPR 25:2021, Vehicles, boats and internal combustion engines, Radio disturbance characteristics: webstore.iec.ch
• UNECE, UN Regulation No. 10 (electromagnetic compatibility), consolidated text Revision 6: unece.org

Specifications and truck reports

The specifications and available CISPR 25 classes for our LED lighting can be found directly on the product pages. Would you like to view a specific truck report to check which measurement methods were used? Please contact TRALERT®’s product specialists.