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CAN CGSB 4.2 No. 26.3-2010: Determination of Colourfastness to Light Using a Xenon-Arc Lamp – Technical Overview
A comprehensive guide to the Canadian standard for artificial light colourfastness testing in textiles
CAN CGSB 4.2 No. 26.3-2010, part of the CGSB 4.2 series of textile test methods, specifies a procedure for determining the resistance of the colour of textiles to the action of an artificial light source. The standard employs a xenon-arc lamp fitted with appropriate filters to simulate natural daylight (D65). It is applicable to all types of textile materials, including those containing fluorescent whitening agents, and is widely adopted in Canada and internationally for quality assurance, product certification, and regulatory compliance. This article provides a detailed examination of the scope, technical requirements, implementation considerations, and compliance aspects of the standard.
Scope and Application
The scope of CAN CGSB 4.2 No. 26.3-2010 encompasses the determination of the colourfastness of textiles to artificial light at moderate humidity and temperature. The method is intended to simulate the photodegradation that occurs during natural exposure while providing a controlled, reproducible acceleration. The standard is applicable to a wide range of textile materials—woven, knitted, nonwoven, and coated fabrics—and to dyed, printed, or otherwise coloured articles. It is typically used for:
- Internal quality control during production
- Qualification of new dyes and finishes
- Product certification and labelling (e.g., UV resistance ratings)
- Comparative evaluation between suppliers or batches
Although national in origin, the standard is harmonised with the international standard ISO 105-B02:1994/Amd 2:2000, enabling Canadian manufacturers to align with global trade requirements while retaining specific national adaptations. The test method is often cited in procurement specifications for automotive textiles, apparel, upholstery, and technical fabrics.
Technical Requirements and Test Methodology
Apparatus and Instrumentation
The core apparatus is a xenon-arc lamp system capable of maintaining the spectral distribution of daylight. The lamp must be filtered (e.g., with borosilicate or soda-lime glass) to remove radiation below 290 nm and to approximate the D65 illuminant. The test chamber must be equipped with:
- A rotating specimen rack to ensure uniform exposure
- A black standard thermometer (BST) or black panel thermometer (BPT) to measure the temperature of the specimen surface
- A humidity control system (for controlled-humidity runs)
- A radiometer or photodiode to monitor and control the irradiance level
Calibration of the irradiance sensor and temperature probe is mandatory at intervals defined by the equipment manufacturer, but at least once every 500 hours of operation or every six months, whichever comes first.
Test Specimens and Reference Materials
Specimens are prepared by mounting the fabric (cut to the size required by the apparatus) on a non-reactive backing card. For each test, a set of blue wool references (grades L2 to L9) is mounted alongside the specimens. These authenticated reference materials are crucial because the exposure endpoint is determined by the change in colour of the references, not by a fixed time interval. The blue wools are calibrated to produce a defined contrast (i.e., Grade 4 on the grey scale for colour change) after a specific exposure dose.
Exposure Conditions
The standard prescribes a set of reference conditions that must be achieved and maintained throughout the test. These conditions are chosen to represent a standard indoor exposure scenario:
| Parameter | Standard Condition | Tolerance |
|---|---|---|
| Irradiance at 420 nm | 1.10 W/(m²·nm) | ± 0.05 W/(m²·nm) |
| Black Standard Temperature (BST) | 65 °C | ± 3 °C |
| Relative Humidity (in-chamber) | 40 % | ± 5 % |
| Spectrum | Daylight (D65) via filter | Both lamp age and filter cleanliness affect spectrum |
The exposure is run continuously (light-only cycle) unless the specific end-use requires a cycle with dark periods or water spray (e.g., for outdoor weatherability). The test proceeds until the contrast between the exposed and unexposed parts of the relevant blue wool reference reaches a grey scale rating of 4 (for the standard endpoint) or 3 (if the user desires a faster comparison).
Evaluation of Colour Change
After exposure, the test specimen is removed and conditioned under standard atmospheric conditions (21 ± 1 °C, 65 ± 2 % RH) for at least 4 hours. The colour change is assessed against the original (unexposed) portion of the same specimen using the grey scale for colour change (ISO 105-A02 or ASTM D2616). The rating is expressed as a number from 5 (no change) to 1 (severe change).
Tip: When evaluating specimens containing fluorescent whitening agents (FWAs), use a viewing cabinet with illumination that includes UV (e.g., D65 with UV component) to ensure that the optical brightening effect is properly accounted for.
Warning: The relative humidity in the test chamber must be controlled precisely. Even a temporary deviation of more than ±5% can alter the fading rate of sensitive dyes, leading to irreproducible results. Install a data logger to verify humidity stability throughout the exposure.
Implementation and Quality Assurance
Laboratories implementing CAN CGSB 4.2 No. 26.3-2010 should establish a robust quality system covering the following aspects:
- Calibration: Regularly verify the irradiance sensor against a reference radiometer traceable to a national metrology institute. The black standard thermometer should be calibrated against a certified thermometer at least annually.
- Reference Materials: Purchase blue wool references from approved suppliers and store them in a cool, dark, dry environment. Record the lot number and expiry date. Use fresh references for each series of tests.
- Apparatus Maintenance: Replace the xenon lamp after the recommended lifetime (typically 1500–2000 hours) and clean the filters according to the manufacturer’s instructions. Any degradation in lamp output below the required irradiance level invalidates the test.
- Control Runs: Periodically run a control specimen (e.g., a standard dye with known lightfastness) to verify the system performance. Plot the results on a control chart to detect drift.
Many Canadian testing laboratories operate under an ISO/IEC 17025 accreditation scheme, and this standard is often included in the scope of accreditation. Adherence to the technical requirements and documentation of all calibration and maintenance activities is essential for maintaining accreditation.
Success: Combining the methodology of CAN CGSB 4.2 No. 26.3-2010 with the globally recognised ISO 105-B02 allows Canadian textile companies to satisfy both domestic customer specifications and export market demands, reducing duplicate testing.
Danger: Using expired or improperly stored blue wool references is a common source of erroneous ratings. The reference materials are sensitive to heat, humidity, and light; even short exposure to ambient conditions can shift their fading threshold, leading to over- or under-rating of the specimen.
Compliance and Industry Relevance
Compliance with CAN CGSB 4.2 No. 26.3-2010 is not a legal requirement unless explicitly referenced in a regulation or procurement document. However, many Canadian retailers and government agencies require textile suppliers to provide test reports based on this standard. For example, the Government of Canada’s Green Procurement policy may reference this standard for textiles used in office furnishings and uniforms. Similarly, automotive manufacturers like FCA Canada often call up a variant of this method for interior trim materials.
The test method can be used in product labelling schemes that declare lightfastness levels (e.g., “UV Resistance Rating 5” based on blue wool scale). The standard is also referenced in the CAN/CGSB-4.2 series as a companion to No. 26.2 (carbon-arc) and No. 26.4 (high-humidity lightfastness). Laboratories should be prepared to advise clients on which specific conditions (irradiance, temperature, cycle) best simulate the intended end-use environment.
FAQs
Q: What is the primary difference between CAN CGSB 4.2 No. 26.3-2010 and ISO 105-B02?
A: The two standards are technically equivalent in terms of apparatus, specimen preparation, exposure conditions, and evaluation. CAN CGSB 4.2 No. 26.3-2010 includes additional national notes that address Canadian climate considerations (e.g., lower UV levels and cooler temperatures) and may specify alternative exposure times for certain end-uses. In practice, a test performed according to ISO 105-B02 is considered compliant with the Canadian standard.
A: The two standards are technically equivalent in terms of apparatus, specimen preparation, exposure conditions, and evaluation. CAN CGSB 4.2 No. 26.3-2010 includes additional national notes that address Canadian climate considerations (e.g., lower UV levels and cooler temperatures) and may specify alternative exposure times for certain end-uses. In practice, a test performed according to ISO 105-B02 is considered compliant with the Canadian standard.
Q: Can this standard be applied to textiles that contain fluorescent whitening agents (FWAs)?
A: Yes, the standard explicitly covers textiles with FWAs. However, the assessment of colour change must account for the fact that FWAs can be photo-degraded or activated differently under xenon-arc light. The evaluation should be performed under a light source that includes UV radiation (e.g., D65) to accurately reflect the visual impact. Some laboratories choose to evaluate both the change in colour and the change in whiteness (using a spectrophotometer) to capture the effect.
A: Yes, the standard explicitly covers textiles with FWAs. However, the assessment of colour change must account for the fact that FWAs can be photo-degraded or activated differently under xenon-arc light. The evaluation should be performed under a light source that includes UV radiation (e.g., D65) to accurately reflect the visual impact. Some laboratories choose to evaluate both the change in colour and the change in whiteness (using a spectrophotometer) to capture the effect.
Q: How long does a typical test take to complete?
A: Exposure time depends on the lightfastness of the fabric and the desired endpoint. For a moderately lightfast fabric (blue wool rating of L4), the exposure to reach a contrast of grey scale 4 may take about 40–60 hours of continuous light at the standard irradiance. For more durable materials (L7 or higher), the test may extend to 200–300 hours. The standard allows the user to define a fixed exposure time if the endpoint is based on a predetermined dose rather than a blue wool reference.
A: Exposure time depends on the lightfastness of the fabric and the desired endpoint. For a moderately lightfast fabric (blue wool rating of L4), the exposure to reach a contrast of grey scale 4 may take about 40–60 hours of continuous light at the standard irradiance. For more durable materials (L7 or higher), the test may extend to 200–300 hours. The standard allows the user to define a fixed exposure time if the endpoint is based on a predetermined dose rather than a blue wool reference.
Q: How should I interpret a grey scale rating of 3–4 in a test report?
A: A rating of 3–4 indicates a moderate but acceptable change for many interior applications. The rating is the average of two intermediate steps (3 and 4) if the evaluator determines the change is between these two grades. Final acceptance of such a rating depends on the product specification; for high-end automotive interiors, a rating of 4 or higher is typically required, while for disposable textile items, a rating of 3 may be acceptable.
A: A rating of 3–4 indicates a moderate but acceptable change for many interior applications. The rating is the average of two intermediate steps (3 and 4) if the evaluator determines the change is between these two grades. Final acceptance of such a rating depends on the product specification; for high-end automotive interiors, a rating of 4 or higher is typically required, while for disposable textile items, a rating of 3 may be acceptable.
By adhering to the guidelines set forth in CAN CGSB 4.2 No. 26.3-2010, textile professionals can ensure reliable, reproducible lightfastness assessments that support quality products and informed purchasing decisions. As of 2026, this standard remains a cornerstone of colourfastness testing in Canada and continues to evolve through periodic review by the CGSB committee on textile test methods.