Optical Distortion Test — UNECE R43 / ISO 3538

What Is Optical Distortion?

The optical distortion test measures how much an image is distorted when viewed through vehicle glass. Two basic quantities are evaluated: optical deviation (the glass bending the image) and secondary-image separation (double imaging, especially in laminated glass). Since it directly affects the driver's view quality, it is part of type approval.

Purpose of Optical Distortion

The purpose is to verify that the glass does not distort the driver's view to an unacceptable degree, and to produce the evidence required for type approval.

Which Products Is Optical Distortion Applied To?

Windscreens (laminated)
Side and rear glass
Glass roofs
Glass incorporating a head-up display area

In Which Sectors Is Optical Distortion Used?

AutomotiveGlass

Standards Related to Optical Distortion

UNECE R43safety glasses test
ISO 3538
ANSI Z26.1

Optical Distortion Conditions

Viewing angle: Set according to the glass's mounting angle on the vehicle
Measurement zones: In the vision-field zones defined by the standard (zones A and B)
Projection distance: Target and screen placement at the distance prescribed by the standard

Equipment for Optical Distortion

Optical distortion test rig (projection system)
Target patterns and screen
Secondary-image measurement rig
Angle-adjustable specimen holder
Measurement and image-analysis system

Sample Requirements for Optical Distortion

Complete glass specimens representing series production
The glass mounting angle and vision-field zones must be defined
Coating, heating-wire and banded zones must be stated
The specimen must be clean and unscratched

Duration of Optical Distortion

The measurement is short per specimen; together with zone definition and rig setup, the result is obtained within a few days.

Optical Distortion Procedure

1The specimen description and mounting angle are recorded.
2The glass is placed in the rig at its angle as installed in the vehicle.
3Vision-field zones are marked.
4A target pattern is projected through the glass onto the screen.
5Optical deviation is calculated by measuring the distortion in the pattern.
6Secondary-image separation is measured.
7Results are reported by zone.

Optical Distortion Acceptance Criteria

The acceptance criterion is defined by zone in UNECE R43: the maximum permitted angular values for optical deviation and secondary-image separation are given in the standard's relevant annex. Requirements are stricter for zone A (the driver's primary vision field).

Evaluation of Results

Measurements are evaluated separately by vision-field zone. Distortion increases in edge regions where the glass's curvature radius is small; correctly determining zone boundaries therefore directly affects the result.

Optical Distortion Report

Applied standard and annex
Specimen description and mounting angle
Vision-field zone definitions
Optical-deviation values by zone
Secondary-image separation measurements
Comparison with limit values

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

UNECE R43
Vehicle type-approval legislation

Otomotiv Testleri — What Does This Testing Field Cover?

The section below describes the field that the Optical Distortion test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Automotive testing shows that a component keeps working under conditions representing the loads it will meet over the life of the vehicle. A vehicle is not a single product but an ENVIRONMENT: vibration, temperature cycling, salt water, stone impact, electrical transients and electromagnetic noise are all present at the same time and for years.

What distinguishes this family is that VEHICLE MANUFACTURER SPECIFICATIONS sit on top of the standards. ISO and SAE publications establish the common ground; but Volkswagen, BMW, Ford, Stellantis, Toyota and Renault define different severity levels, additional tests and different acceptance criteria in their own specifications. For a component, the phrase "complies with automotive standards" is not sufficient on its own; which manufacturer's specification, and which revision of it, must be answered.

The family carries three separate processes together and they are often confused. Homologation covers the type approvals a vehicle needs to enter traffic and runs under state authority. Supplier approval means passing the vehicle manufacturer's own quality and testing requirements and is a commercial relationship. The third is design verification: the engineering team demonstrating that its own design meets its targets.

At component level the test plan is built around the LOCATION OF USE. A module in the engine bay and a module in the boot do not go through the same temperature and vibration profile; a component inside a door and one in the roof console do not see the same water and dust exposure. The ISO 16750 series is the common framework for this location-based approach.

The shift to electric vehicles has reshaped the field. High-voltage safety, insulation coordination, battery safety, charging interface conformity and the electromagnetic behaviour of high-voltage components have been added to the classical automotive test set. In a quiet vehicle, acoustic and vibration expectations have changed too; sounds once masked by the combustion engine are now audible.

The quality system side cannot be separated from testing in this field. A manufacturer under IATF 16949 presents test results in the PPAP file; measurement system analysis, process capability study and the control plan stand around the test report. A single good result is not enough — the process must be shown to be able to repeat it.

Method groups in this field

Environmental and climatic
Temperature cycling, thermal shock, damp heat, salt spray, dust and water ingress (IP), solar radiation. Severity levels vary with the mounting location.
Mechanical
Sine and random vibration, shock, mechanical loads, fastener torque and durability cycles.
Electrical
Supply voltage variations, transients (ISO 7637), reverse polarity, overvoltage, short circuit and sleep current measurements.
EMC
Component emissions (CISPR 25), radiated and conducted immunity (ISO 11452 series), electrostatic discharge (ISO 10605).
Materials and emissions
Odour, fogging and VOC emissions from interior materials; flammability; UV ageing; coating durability and stone impact.
Functional safety and cyber security
Functional safety evidence under ISO 26262 and cyber security engineering under ISO/SAE 21434; these are tied to regulation through UNECE R155 and R156.

Commonly confused in this field

An automotive report without a specification reference is not accepted in the supply chain; which OEM specification and revision was applied must be stated.
Type approval and supplier approval are different processes. A component with E-Mark approval is not thereby considered to have passed the OEM's own acceptance tests.
A result obtained on a prototype does not carry over to series production; PPAP is done with series production parts.
On the EMC side, measuring emissions alone is incomplete; immunity is a separate body of work and is more critical in a vehicle.
On electric vehicle components, high-voltage safety is a distinct competence; classical 12 V test infrastructure is not sufficient.

Which decisions these results support

Supplier component approval and the PPAP file
UNECE type approval and E-Mark marking
Design verification and durability evidence
Root cause analysis of field complaints and warranty returns
Assessing the impact of a design or supplier change

Related Tests

Frequently Asked Questions About Optical Distortion

Why does a secondary image occur?

It arises from the separation of reflections coming from the front and back surfaces in laminated glass. The two glass surfaces not being exactly parallel enlarges this separation; it is noticed as a double image with oncoming headlights at night.