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CAN CGSB 4.2 No. 25.2-M89 (2013): Colourfastness to Light – Xenon Arc Lamp Test for Textiles
Comprehensive technical overview of the Canadian standard for evaluating textile colourfastness under artificial light exposure
CAN CGSB 4.2 No. 25.2-M89 (2013) is a Canadian national standard developed by the Canadian General Standards Board (CGSB) that specifies a method for determining the resistance of textile colour to the action of artificial daylight. Originally published in 1989 and reaffirmed in 2013, the standard is widely recognized in the textile industry for assessing lightfastness under controlled conditions using a xenon arc lamp as the light source.
Scope and Purpose
This standard applies to all types of textile materials, including woven, knitted, nonwoven, and coated fabrics, regardless of their fibre composition or colour application (dyeing, printing, finishing). The test method is designed to simulate the spectral distribution of natural daylight in the ultraviolet and visible regions. It is intended for routine quality control, research, and product certification purposes.
The method is particularly suitable for materials that will be exposed to intense sunlight during their end use, such as automotive interiors, outdoor apparel, upholstery, and architectural textiles. However, it may not fully represent the effects of sunlight through window glass (which filters UV) or extreme environmental conditions (e.g., high humidity, salt spray). For such cases, supplementary test methods (e.g., CGSB 4.2 No. 25.3 or relevant ASTM standards) should be considered.
Note: The standard is technically equivalent to ISO 105-B02 (Colourfastness to artificial light: Xenon arc fading lamp test), which facilitates international harmonization of lightfastness testing for textile products.
Technical Requirements
The test method prescribes specific instrument, calibration, and environmental conditions to ensure reproducibility and comparability of results.
Xenon Arc Lamp and Filters
A water-cooled or air-cooled xenon arc lamp is used as the light source. The spectral power distribution shall simulate natural daylight (CIE D65) in both the UV and visible regions. The standard requires the use of suitable filters to achieve the required cut-off wavelengths:
- Option A: Borosilicate glass filters (simulating daylight through window glass) – irradiance at 420 nm typically 1.10 W/m².
- Option B: Outer quartz filters with inner soda lime glass filters (for special applications) – must be specified in the test report.
Exposure Conditions
The standard defines two sets of exposure conditions for routine testing. The following table summarises the primary requirement:
| Parameter | Condition | Tolerance |
|---|---|---|
| Black Standard Temperature (BST) | 74 °C | ± 2 °C |
| Black Panel Temperature (BPT) | 65 °C | ± 3 °C |
| Relative Humidity (RH) in chamber | 50% | ± 5% |
| Irradiance at 420 nm | 1.10 W/m² (recommended) | ± 0.05 W/m² |
| Specimen size (min.) | 70 mm × 120 mm | – |
Blue Wool Reference Standards
To standardise exposure levels, the method employs a set of eight blue wool references (Shades 1 to 8) that fade in a defined logarithmic progression. The test is run until a specific contrast is observed on the reference (e.g., Grade 4 fading on the grey scale) and then graded accordingly. The references are used either as a control for exposure duration or as a direct comparison for the test specimen.
| Blue Wool Grade | Lightfastness Rating | Typical End Use |
|---|---|---|
| 1 | Very low | Disposable items |
| 2–3 | Low to moderate | Clothing with limited light exposure |
| 4–5 | Good | General apparel, curtains |
| 6–7 | Very good | Automotive interior fabrics, outdoor gear |
| 8 | Excellent | Architectural fabrics, awnings |
Important: Calibration of the irradiance sensor, black panel/black standard thermometer, and humidity sensor must be performed at least every 500 hours of lamp operation or in accordance with the instrument manufacturer’s instructions. Failure to calibrate can lead to significant variations in test results.
Implementation Highlights
Successful implementation of the test method requires careful attention to sample preparation, mounting, and exposure control.
Sample Preparation and Mounting
Samples are cut to the specified size and conditioned at 20 °C ± 2 °C and 65% ± 4% relative humidity for at least 4 hours prior to testing. Each specimen is mounted on a white card (minimum reflectance 80%) and placed in a specimen holder that ensures uniform air circulation. Multiple specimens can be exposed simultaneously, but a covered standard (e.g., blue wool) must be included in each run.
Exposure Cycles and Termination
The exposure cycle consists of alternating light-only and light-plus-dark phases to simulate real-world diurnal cycles. A typical cycle is 102 minutes light-only followed by 18 minutes light and water spray (simulating rainfall) if wetting is required. The test is terminated when the blue wool reference shows a change equal to Grey Scale Grade 4 for the desired endpoint (e.g., Grade 6 fading on no. 6 blue wool indicates lightfastness 6).
Evaluation
After exposure, specimens are conditioned in the dark at ambient conditions for at least 1 hour before assessment. Colour change is evaluated against the standard grey scale for assessing change in colour (ISO 105-A02). The rating is performed under a D65 illuminant with a colour temperature of 6500 K, at a 45°/0° observation geometry. The rating may also be expressed as a numerical grade from 1 (very poor) to 8 (excellent) using the blue wool scale.
Good practice: Keep a record of all exposure parameters (temperature, humidity, irradiance, cycle times) and operator notes. Many certification bodies require traceability logs to ensure compliance with the standard.
Compliance and Quality Assurance
Adherence to CAN CGSB 4.2 No. 25.2 is mandatory for textiles intended for use in federal government procurement in Canada when lightfastness is specified. However, the standard is also widely adopted by private-sector manufacturers and testing laboratories.
Certification and Testing
Accredited laboratories can perform the test and issue test reports in accordance with the standard. While the standard does not define pass/fail criteria, it is common for buyers or specifiers to require a minimum lightfastness rating (e.g., ≥ 5 for automotive fabrics). The test report must include all relevant test conditions, the light source option used, the type of blue wool references, and the final rating(s).
Interlaboratory Comparisons
Because lightfastness testing is influenced by many variables (lamp age, cleanliness of filters, calibration accuracy, temperature gradients), regular participation in round-robin exercises is recommended to validate laboratory competence. The standard itself provides a procedure for interlaboratory comparison using a reference material (e.g., red wool).
Caution: Never use a xenon lamp beyond its recommended service life without recalibration. The spectral distribution shifts over time, especially in the UV region, which can lead to erroneous test results that over- or under-estimate lightfastness.
Documentation and Record Keeping
All calibration certificates, exposure records, and test results should be retained for a period defined by the quality system (commonly 5–10 years). Digital dataloggers can simplify this process, but manual logs must be legible and signed by the responsible technician.
Q: What is the difference between CAN CGSB 4.2 No. 25.2-M89 and ISO 105-B02?
A: The two standards are technically equivalent in terms of test conditions, equipment, and evaluation. The main difference lies in the administrative framework and the specific references to Canadian standards. Laboratories already accredited to ISO 105-B02 can easily demonstrate compliance with CAN CGSB 4.2 No. 25.2 with minor adjustments to reporting.
A: The two standards are technically equivalent in terms of test conditions, equipment, and evaluation. The main difference lies in the administrative framework and the specific references to Canadian standards. Laboratories already accredited to ISO 105-B02 can easily demonstrate compliance with CAN CGSB 4.2 No. 25.2 with minor adjustments to reporting.
Q: Can this test be used for all textile types, including lightweight fabrics and pile fabrics?
A: The standard covers most textiles, but lightweight or pile fabrics may require special mounting procedures to prevent curling or shading. For pile fabrics, the standard suggests mounting with the pile direction perpendicular to the light source. The test report must describe any deviations from the standard procedure.
A: The standard covers most textiles, but lightweight or pile fabrics may require special mounting procedures to prevent curling or shading. For pile fabrics, the standard suggests mounting with the pile direction perpendicular to the light source. The test report must describe any deviations from the standard procedure.
Q: How does the test simulate natural sunlight?
A: The xenon arc lamp, combined with appropriate optical filters, produces a spectrum that closely matches natural daylight (CIE D65) in the UV and visible ranges. The use of filters such as borosilicate glass ensures that the energy distribution in the UV-A and UV-B bands is representative of natural sunlight through window glass, making it suitable for indoor and automotive applications.
A: The xenon arc lamp, combined with appropriate optical filters, produces a spectrum that closely matches natural daylight (CIE D65) in the UV and visible ranges. The use of filters such as borosilicate glass ensures that the energy distribution in the UV-A and UV-B bands is representative of natural sunlight through window glass, making it suitable for indoor and automotive applications.
Q: What are the most common issues encountered during testing?
A: Common issues include uneven irradiance across the exposure plane, temperature and humidity fluctuations due to poor chamber design or calibration drift, and incorrect handling of blue wool references. To mitigate these, the standard recommends using a rotating specimen rack, regular monitoring of environmental conditions, and periodic check of the blue wool references’ fading behaviour.
A: Common issues include uneven irradiance across the exposure plane, temperature and humidity fluctuations due to poor chamber design or calibration drift, and incorrect handling of blue wool references. To mitigate these, the standard recommends using a rotating specimen rack, regular monitoring of environmental conditions, and periodic check of the blue wool references’ fading behaviour.