Overview
ISO 2135:2024 specifies an accelerated artificial‑light test method for assessing the light fastness of coloured anodic oxidation (anodized) coatings on aluminium and its alloys. Intended mainly as a quality‑control tool, the standard defines exposure devices, reference materials, specimen preparation and assessment procedures (visual and instrumental) to assign a light fastness number. The document is the fifth edition (2024) and updates the 2017 version.
Key topics and requirements
- Scope and purpose
- Accelerated testing using artificial light is suitable for QC of coloured anodic coatings whose outdoor-established light fastness number is already known. Outdoor exposure (ISO 105‑B01) is the definitive method for exterior durability.
- Not suitable for coatings with an outdoor-established light fastness number < 6.
- Apparatus and reference materials
- Acceptable light sources: xenon‑arc lamp, open‑frame carbon‑arc or enclosed carbon‑arc (specifications in Annex A).
- Blue wool reference materials (1–8) per ISO 105‑B02 and the grey scale per ISO 105‑A02 are required.
- Opaque cardboard for masking and measurement instruments for instrumental assessment (colour meter per ISO 4582).
- Specimen preparation
- Representative flat specimens (standard ~150 mm × 70 mm) cleaned and prepared exactly as the product (same alloy, pre‑treatment, anodizing, colouring and sealing).
- Exposure conditions
- Specimens are positioned equidistant from the light source and revolved or relocated to ensure uniform exposure.
- Black panel temperature: (63 ± 3) °C (or (50 ± 3) °C by agreement).
- Assessment and results
- Calibrate exposure cycle using blue wool reference material 6: exposure cycle = time to reach grade 3 on the grey scale (≈25% loss).
- Visual assessment: number of exposure cycles mapped to a light fastness number (e.g., 1 cycle → 6; 2–3 → 7; 4–7 → 8; 8–15 → 9; 16 → 10; >16 → >10).
- Instrumental assessment: report ΔE* (ISO 4582) and, if needed, gloss retention (ISO 7668).
- Test report
- Must include reference to ISO 2135:2024, material and finishing details, light source type, results, deviations and test date.
Applications and users
- Quality control and production testing in anodizing plants and surface‑finishing workshops.
- Independent testing laboratories performing accelerated lightfastness evaluation.
- Material engineers, specifiers, OEMs, architects and façade manufacturers verifying colour durability of anodized aluminium components.
- Useful for contract compliance, batch acceptance, and comparative evaluation of coloured anodic coatings.
Related standards
- ISO 105‑B01 (daylight outdoor exposure)
- ISO 105‑B02 (xenon arc artificial light / blue wool references)
- ISO 105‑A02 (grey scale for assessing change in colour)
- ISO 4582 (instrumental colour change, ΔE*)
- ISO 7583 (anodizing terms and definitions)
- ISO 7668 (gloss retention)
Keywords: ISO 2135, anodizing of aluminium, anodic oxidation coatings, light fastness, accelerated test, xenon‑arc, carbon‑arc, blue wool, grey scale, ΔE*.