Carbon Arc Lamp Weathering Test for Automotive Components: Standards, Methods, and Applications

Carbon arc lamp aging testing is a proven accelerated weathering method used to evaluate the durability of automotive components against light, heat, and moisture exposure. By simulating years of outdoor service conditions in a compressed laboratory timeframe, this test helps manufacturers verify material performance, predict product lifespan, and meet OEM specification requirements. This article provides a comprehensive overview of carbon arc lamp aging test standards, sample types, testing procedures, and evaluation methods for automotive parts.

Technical Overview

Carbon arc lamp aging testing is an accelerated weathering technique that exposes automotive components to intense artificial light generated by carbon arc lamps, combined with controlled temperature, humidity, and water spray cycles. Originally developed in the early 20th century, carbon arc technology remains widely referenced in automotive industry specifications, particularly those originating from Japanese vehicle manufacturers, where it served as the foundation for many material qualification programs.

The carbon arc produces a spectral distribution with strong ultraviolet (UV) output and visible radiation that accelerates the photodegradation processes occurring in polymers, coatings, rubber, and textiles during natural outdoor exposure. During testing, an electric current passes between carbon electrodes, generating a high-intensity arc. The resulting radiation, filtered through borosilicate glass enclosures in enclosed carbon arc systems or used directly in open-flame sunshine carbon arc systems, drives photochemical reactions such as polymer chain scission, oxidation, color fading, and surface embrittlement.

Although xenon arc testing has become increasingly common for many global specifications, carbon arc testing remains essential for compliance with legacy and current standards such as ASTM G152, ASTM G153, and JIS D 0205, which are still invoked in numerous automotive supply chain requirements across Asia, North America, and Europe.

Testing Samples

Exterior Plastic Components

Exterior parts are subjected to the harshest sunlight exposure conditions and represent a primary category for carbon arc aging evaluation. Typical samples include bumper fascias, radiator grilles, side mirror housings, door handles, wheel arch trims, fender extensions, lamp housings and lenses, body moldings, and exterior trim strips produced from materials such as polypropylene (PP), acrylonitrile butadiene styrene (ABS), polyamide (PA), polybutylene terephthalate (PBT), and polycarbonate (PC) blends.

Interior Plastic Components

Interior parts experience solar radiation transmitted through windshield and window glass, which filters out a portion of UV wavelengths while generating significant heat buildup. Samples include instrument panel components, dashboard trim, center console parts, door trim panels, pillar trims, HVAC vents, switch bezels, steering wheel components, and seat trim made from ABS, PP, polypropylene copolymers, thermoplastic olefins (TPO), and polyurethane.

Coatings, Paints, and Films

Automotive coating systems, including base coats, clear coats, primer surfaces, refinish paints, and decorative films, are evaluated for gloss retention, color stability, chalking resistance, and adhesion after carbon arc exposure. Samples may be coated metal panels, coated plastic plaques, or finished component sections.

Rubber and Elastomeric Parts

Elastomeric components such as weatherstrips, window seals, door seals, gaskets, hose materials, tires sidewall compounds, and molded rubber parts are tested for changes in hardness, tensile properties, elongation, and surface cracking following exposure.

Textiles and Flexible Materials

Seat fabrics, headliner materials, convertible top fabrics, safety belt webbing, and synthetic leather (PVC and polyurethane) materials are tested for colorfastness, strength retention, and surface degradation.

Testing Items

Carbon arc lamp aging tests evaluate multiple performance characteristics before and after exposure to quantify material degradation:

• Color change and color difference (Delta E values, evaluated per ISO 7724 or ASTM E1347 using spectrophotometers)
• Gray scale rating for colorfastness assessment (ISO 105-A02)
• Gloss retention and gloss loss (measured per ASTM D523 or ISO 2813)
• Surface appearance evaluation, including chalking, blistering, cracking, crazing, flaking, and staining
• Tensile strength and elongation retention percentage for polymeric materials (ISO 527, ASTM D638)
• Flexural strength and impact strength retention (ISO 178, ISO 179, ASTM D790)
• Hardness change (Shore hardness per ISO 868 or ASTM D2240)
• Visual comparison against unexposed reference specimens and blue wool reference materials
• Fogging and volatile condensation behavior for interior components
• Adhesion strength of coatings and painted layers after exposure

Testing Methods

Carbon arc aging tests follow standardized procedures designed to ensure reproducibility and comparability of results:

Applicable Standards

• ASTM G152: Standard Practice for Operating Open Flame Carbon Arc Light Apparatus for Exposure of Nonmetallic Materials
• ASTM G153: Standard Practice for Operating Enclosed Carbon Arc Light Apparatus for Exposure of Nonmetallic Materials
• JIS D 0205: Japanese standard for weatherability testing methods of automotive parts, widely referenced by Japanese OEM specifications
• ISO 4892-4: Plastics — Methods of exposure to laboratory light sources — Part 4: Open-flame carbon-arc lamps
• ISO 4892-1: General guidance for laboratory light exposure methods

Test Apparatus and Exposure Conditions

Testing is conducted in specialized carbon arc weathering chambers equipped with carbon electrode assemblies, optical filters, specimen racks, temperature control systems, humidity regulation, and programmable water spray nozzles. Typical operating parameters include black panel temperatures ranging from 55°C to 63°C, chamber dry-bulb temperatures between 40°C and 60°C, and relative humidity levels from 50% to 95% depending on the specified cycle.

Common Exposure Cycles

Exposure cycles vary according to the governing standard and OEM specification. Frequently applied cycles include continuous light exposure with periodic water spray (for example, 102 minutes of light followed by 18 minutes of light plus water spray per JIS D 0205), or light-only cycles for interior material simulation. Total exposure durations commonly range from 200 to 2,000 hours, or as specified in terms of cumulative radiant exposure.

Specimen Preparation and Conditioning

Test specimens are prepared from production-grade materials or finished components, typically cut to standardized plaque dimensions or mounted as whole parts when geometry permits. Prior to exposure, specimens are conditioned in controlled atmospheres (usually 23°C and 50% relative humidity per ISO 291) and baseline measurements of color, gloss, and mechanical properties are recorded. Retained control specimens are stored unexposed for post-test comparison.

Post-Exposure Evaluation

After completing the specified exposure period, specimens are removed, conditioned to stabilize their state, and evaluated against baseline data. Instrumental color measurements quantify color difference, gloss meters determine retention percentages, and mechanical testing establishes property degradation. Visual assessments rate surface defects using standardized scales, and results are reported with complete documentation of exposure conditions, cycle parameters, and evaluation methods.

Applications

Carbon arc lamp aging testing serves multiple purposes across the automotive industry value chain:

• Material qualification and approval: Verifying that proposed materials meet OEM weatherability specifications before production release
• New product development: Comparing candidate formulations, additives, UV stabilizers, and pigment systems during design phases
• Quality control: Monitoring production consistency through periodic weatherability verification of outgoing materials
• Supplier certification: Demonstrating compliance with customer technical requirements for exterior and interior component durability
• Root cause analysis: Investigating field failures and validating corrective actions through comparative degradation testing
• Warranty and lifespan prediction: Correlating accelerated exposure hours with years of outdoor service to support durability claims
• Regulatory compliance: Meeting market access requirements where carbon arc methods are specified in national or industry standards
• Competitive benchmarking: Evaluating material performance against incumbent or competitor materials under identical exposure conditions

Accredited third-party laboratories routinely perform carbon arc aging tests for automotive suppliers, tier manufacturers, and OEM engineering departments, providing independent verification that supports both domestic and export market requirements.

FAQ

What is the difference between carbon arc and xenon arc weathering tests?

Carbon arc lamps use an electric arc between carbon electrodes and produce a spectral output with high UV intensity but a different spectral distribution than natural sunlight. Xenon arc lamps, filtered with appropriate optical filters, more closely match full-spectrum sunlight. Carbon arc testing remains specified in many legacy and current standards, particularly Japanese automotive specifications, while xenon arc testing is increasingly common for newer global standards. The choice depends on the governing specification for the material or component.

How many hours of carbon arc exposure correspond to one year of outdoor service?

There is no universal conversion factor, because correlation depends on material type, exposure cycle, geographic climate, and component installation location. Generally, 300 to 500 hours of carbon arc exposure under typical cycles is often considered roughly comparable to one year of outdoor exposure in moderate climates, but this relationship must be validated experimentally for each material system. OEM specifications define required exposure durations based on established correlation data.

What specimen sizes are required for testing?

Standard specimen dimensions typically range from 50 mm × 100 mm to 75 mm × 150 mm plaques for color and gloss evaluation, while mechanical property testing requires dumbbell-shaped specimens cut from exposed plaques per ISO 527 or ASTM D638. Finished components can often be mounted directly when they fit within the specimen rack geometry.

Can carbon arc tests be performed on complete assembled parts?

Yes, complete components such as mirror housings, grilles, door handles, and trim pieces can be exposed when their dimensions accommodate the specimen holder. Testing finished parts evaluates the combined effect of material, surface texture, color, and manufacturing processes, providing a more realistic assessment than flat plaque testing alone.

What information should accompany test samples submitted to a laboratory?

Submissions should include material identification, the governing test standard or OEM specification, required exposure duration or cycle, evaluation criteria and properties to be measured, baseline material data if available, and any special mounting or orientation requirements. Clear specification of these details ensures the test is conducted according to the applicable requirements and produces actionable results.

How should test results be interpreted?

Results are interpreted against the acceptance criteria defined in the applicable specification, which may specify maximum allowable color difference, minimum gloss retention percentages, minimum mechanical property retention, or limits on visual defects such as cracking and chalking. Comparison with retained unexposed control specimens and properly documented exposure conditions supports valid conclusions regarding material weatherability and expected service performance.