LEDr FAQ Hub

This LEDr FAQ hub collects the 25 questions our team hears most often from buyers, engineers and distributors, and answers each one in plain terms with a link to the full guide. If you are sourcing, start with the wholesale group and the buyer checklists. If you handle vehicle integration, go to the fitment and installation groups. If your question is about approval, the certification group summarizes current category status with dates and official documents. Every answer stands on its own, so jump straight to what you need.

Product and fitment

How do I confirm the correct bulb size for my vehicle?

Check the bulb currently installed, the owner’s manual, or a VIN-based parts catalogue, and match the category designation printed on the bulb base, such as H11. The category, not the shape of the housing, decides which light source the lamp was approved with. If your vehicle uses H11 halogen bulbs in approved headlamps, an H11 LEDr is the standardized replacement candidate. Our fitment guide for H11 LEDr explains how the standardized base, envelope and reference plane make this work, and where the exceptions are.

Does the same H11 socket mean any H11 bulb is compatible?

Mechanically, yes for standard types, by design. An H11 LEDr is built on the same standardized PGJ19-2 cap geometry as the H11 filament bulb, so it seats and locks in the same holder. Electrically and optically it is designed to replace the H11 filament source, not merely to fit the hole. The exceptions are defined variants: high-efficiency types, versions with an AE device, single-polarity designs or non-standard dimensions, which must carry vehicle or function lists and installation notes on the packaging. Details are in our H11 fitment guide.

Will an LEDr work in a reflector headlamp?

An approved LEDr is designed to reproduce the position and light distribution of the filament source it replaces, inside the same lamp optics. That equivalence is the condition under which the category is approved, whether the lamp uses a reflector or another optical system. What matters is that the headlamp itself was approved with the corresponding filament category. Dropping a non-approved LED bulb into a reflector housing is a different product class with different risks. Our optical equivalence explainer shows how equivalence is engineered and checked.

Will an LEDr work in a projector headlamp?

The same rule applies as for reflector lamps: approval attaches to the light source category and to lamps approved with the matching filament source, not to one optical layout. A projector headlamp approved with H11 filament bulbs sits inside the intended scope of an H11 LEDr, because the LEDr is engineered to emit from the same reference position with equivalent distribution. Vehicle-level results still depend on correct installation and on the condition of the lamp. See our beam pattern engineering note for what equivalence looks like in measurements.

Do I need to replace the complete headlamp to use LEDr?

No. LEDr exists precisely so that the light source can be replaced inside an already approved lamp. The UN R37 framework defines LEDr as a replacement for a filament light source with the same category designation, for use in lamps approved with that filament category. Replacing the complete headlamp is a different pathway with its own approval logic and cost. The boundaries between replacement, retrofit and substitute products are compared in LEDr vs retrofit vs substitute.

Is there a difference between left-hand and right-hand traffic versions?

The asymmetry of a low beam comes from the headlamp, not from the light source. A filament bulb and its LEDr replacement are built to a common category sheet, while the lamp creates the traffic-side cut-off. Vehicles for left-hand and right-hand traffic use different lamps, and the approved LEDr works inside whichever lamp was approved with the matching filament category. Market-level rules still vary by country, which our European street-legal overview covers separately.

Certification and legal status

What is an LEDr, exactly?

An LEDr, or LED replacement light source, is an LED light source designed to replace a corresponding filament light source that carries the same category designation, while using a different light-generating technology. The concept sits inside the UN R37 approval system: the LEDr shares the category name with its filament counterpart but is approved as a separate type with its own equivalence requirements. It is not a generic label for any LED bulb that fits a socket. The formal definition entered the framework through the UNECE proposal that added LEDr to UN R37, and our LEDr compliance guide walks through the system end to end.

Are all LED bulbs approved for road use?

No. Most LED bulbs sold for halogen sockets have no UN R37 approval at all. Approval exists per category, and the list is short and dated. Verified against UNECE documents on 2026-07-24:

Two boundaries matter. H10, H9, HB3 and HIR2 appear only in informal GRE working material, so they cannot be described or sold as approved categories. H4 and H7 are not listed in R.E.5 Group 5 at all; some countries run national approval schemes based on vehicle compatibility lists, but that is not UN R37 category approval. Category scope is also limited: an LEDr is approved only for use in lamps approved with the same filament category. Our approved categories page tracks this list as it changes.

What does the E-mark on a bulb actually mean?

The international approval mark is a truncated circle containing a capital E followed by a number. The number identifies the contracting party whose authority granted the approval, under the numbering system of the 1958 Agreement, Revision 3; the country codes are listed in R.E.3, Annex 3. Next to the circle sits the approval code identifying the regulation and the approved type. The mark says which authority approved what. It does not say where the product was manufactured, and by itself it does not say which regulation applies. Our E-mark country code explainer has marked-up examples.

Does an E-mark alone make a bulb road legal?

No. The E-mark shows that an authority approved a specific type. Road use depends on more: the approval must cover the correct regulation and category for the application, the lamp must be approved for that light source category, installation conditions must be met, and national rules on inspection and market surveillance still apply. A bulb carrying an approval under an unrelated regulation does not become a road-legal headlamp light source because it has a circle and a number. The full decision path is in Does an E-mark mean road legal?.

How do I verify an approval number before I buy?

Check the complete marking on the light source itself, not only on the box: the E-mark circle, the approval code, the category designation and the LEDr marking. Then ask the supplier for the approval documentation and compare the category, type, applicant, manufacturer, drawings and any extensions against the physical product. Conformity of Production obligations sit behind every approval, so ask how CoP is evidenced. No single public database covers approvals from all contracting parties, so verification rests on documents plus marking. Our step-by-step method is in How to verify an ECE R37 H11 LEDr certificate.

Is an approved LEDr legal in every country?

UN approvals operate inside the 1958 Agreement framework of mutual recognition between contracting parties. That framework is the starting point, not the finish line. The light source approval covers the category; the lamp approval covers the headlamp; installation rules and national inspection practice cover the vehicle. Some markets add their own requirements, and enforcement practice differs. The UNECE status page for the 1958 Agreement shows which states apply which regulations. For the European picture, read Is an ECE R37 LEDr street-legal across Europe?.

What is the difference between R37 and R10?

They regulate different things. UN R37 type-approves light sources: category sheets, photometric, geometric and thermal requirements, and the LEDr equivalence framework. UN R10 covers electromagnetic compatibility for electrical and electronic sub-assemblies. An LEDr must meet the applicable R10 requirements as one part of its R37 approval, but R10 alone proves nothing about optics or category. A bulb marked only to R10 is not shown to be an R37 LEDr, and UNECE working material treats wrong-regulation marking presented as road approval as a non-compliance case. Current texts: UN R37, Revision 7, Amendment 11 and UN R10, Revision 6.

Are CE and RoHS enough for road use?

No. CE marking and RoHS address EU product safety declarations and hazardous-substance restrictions for placing goods on the market. Neither is a vehicle light source type approval. Road use of a replacement light source in 1958 Agreement markets is a homologation question: category, approval documents, marking and lamp conditions. A supplier offering CE and RoHS as the whole compliance file has not answered the homologation question at all. The difference between product testing and type approval is explained in Type approval vs product testing.

Installation and electrical

Is LEDr installation plug and play?

Physically, usually yes: the standardized cap, envelope and reference plane are designed so the LEDr seats where the filament bulb sat. Two cautions keep this honest. Plug-and-play describes design fit, not a road-use conclusion; legality still depends on the approval chain described in the certification group above. And vehicle electronics may react to the different current draw of an LED, which is an integration topic, not a defect. Our plug-and-play explainer separates the design layer from the legal layer.

Do I need a CANBUS decoder?

Sometimes. Many vehicles monitor the filament bulb circuit and interpret the different current draw of an LED as a failed bulb, triggering warnings or changing behavior such as pulsing. CANBUS-adapted designs and external decoders exist to satisfy that monitoring. Whether you need one depends on the vehicle, not on the approval status of the bulb. An approved LEDr can still trip a bulb monitor on a specific car, and an unapproved bulb with a decoder is still unapproved. Vehicle-side questions are covered in our H11 fitment guide.

Why does my LED bulb flicker?

Flicker usually has an electrical cause, not a light-source defect. Common triggers are bulb monitoring circuits sending pulse checks the LED cannot absorb smoothly, voltage instability at the connector, or a marginal driver design reacting to temperature. Diagnose in order: note the flicker pattern, check whether it changes with engine state, and test with the vehicle’s monitoring system in mind. Persistent flicker on an approved LEDr installed correctly is a supplier quality question worth raising through warranty channels. Our voltage and temperature behavior note explains the mechanisms.

Why does the dashboard show a bulb error after installation?

Because the car is looking for a filament bulb. Monitoring systems measure resistance or current and flag values outside the expected band. An LED draws differently by design, so a vehicle without adaptation may report a fault even while the lamp works. The fix sits on the vehicle side: CANBUS-adapted bulb variants, decoders, or coding where the manufacturer supports it. A dashboard error is not evidence that the bulb failed, and clearing the error does not change whether the product is approved. See our warranty and failure analysis guide for triage steps.

Can LED bulbs interfere with radio or GPS reception?

Any electronic device can emit electromagnetic noise, which is why electromagnetic compatibility requirements exist. An LEDr approved under UN R37 must meet the applicable UN R10 requirements for electronic sub-assemblies, which set emission and immunity limits. A bulb that causes audible interference on the radio or degrades GPS reception is a warning sign about its EMC performance, and possibly about what it was actually tested against. Ask suppliers which R10 test reports sit behind the product. The regulatory split is explained in the R37 vs R10 answer above, and our glossary defines the terms.

Do the headlamps need re-aiming after installing LEDr?

An approved LEDr is designed to emit from the same reference position as the filament source it replaces, so correct installation should leave the beam geometry where the lamp design put it. Headlamp aim is a vehicle-level setting, and checking it after any bulb service is normal workshop practice and part of periodic inspection in many markets. If the beam pattern visibly changed after installation, something is wrong: seating, lamp condition, or the product itself. Our beam pattern explainer shows what a correct pattern looks like.

Wholesale and customization

Do you offer OEM and private label programs?

Yes, within the approval framework. Private label arrangements in this product class run through the approval’s own procedures: trademark variants and extensions must be traceable in the approval documentation, with the approval holder, manufacturer and type correctly linked. A distributor cannot simply borrow a certificate; the paperwork has to reflect the actual branding chain. Program scope, artwork responsibilities and timelines are commercial details we handle case by case. Background reading: Private label H11 LEDr launch guide.

What is the minimum order quantity?

MOQ depends on the program. Standard catalog models, customized packaging and private label projects each carry different thresholds because tooling, printing and documentation work differs. We quote MOQ together with lead time and quality control checkpoints as one package, so you can compare total cost rather than a unit price alone. Send your target volume and customization level for a concrete answer. Our MOQ, lead time and QC guide explains how the numbers are built.

Which documents should we request before placing an order?

Ask for the approval documentation behind the product: certificate copies tied to the correct category and type, the applicant and manufacturer details, extension records where brands vary, and evidence of how Conformity of Production is maintained. Add the test reports that support electrical and EMC claims, and the packaging artwork with its required markings. Compare every document against physical samples before committing. Our supplier documents checklist lists the file set we recommend importers hold.

Can you supply packaging with our brand?

Yes, with one regulatory condition. The packaging of an approved LEDr must carry defined elements: the trademark, rated voltage, the category designation with the LEDr marking, and the approval code, plus additional information symbols and instructions where the design has specific conditions. Brand customization operates inside those marking requirements, not instead of them. We prepare artwork proofs against the approval documents so the printed box matches the approved type. Practical details are in our OEM packaging guide.

How do warranty and RMA work for B2B orders?

Warranty terms are set per program and confirmed in the sales contract, covering manufacturing defects under normal use. The RMA flow is evidence-based: report the failure mode, provide installation and vehicle context, and return samples for analysis so application issues can be separated from product issues. Failure analysis findings feed back into production and, where relevant, into Conformity of Production records. Our warranty and failure analysis guide describes the process from the buyer side.

What should importers verify?

Verify the category is approved under UN R37, the complete marking on the light source, the approval documents and holder, and the lamp and vehicle conditions. The full path is in our LEDr compliance guide.

What is the next step for B2B buyers?

Confirm your category, download the buyer checklist, request approval documents from shortlisted suppliers, then review the H11 LEDr product page for models and OEM terms.

Author: Jack Liu — Co-founder & Product Director, LEDOAUTO
Regulatory review: LEDOAUTO Engineering Team — verified against official UNECE documents
Last reviewed: 2026-07-24