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CAN CGSB 4.2 No. 73.2-M91 (2013): Colourfastness to Light — Xenon Arc Fading Lamp Test Method
A comprehensive technical guide to the Canadian standard for evaluating textile colourfastness under artificial light exposure
Scope and Application
CAN CGSB 4.2 No. 73.2-M91 (2013) is part of the CAN/CGSB-4.2 series of standard test methods for textiles. This standard specifies a method for determining the colourfastness of textile materials to the action of artificial light using a xenon arc fading lamp. The test simulates the degradation effects of natural daylight, including ultraviolet radiation, and is applicable to all types of textiles—dyed, printed, or otherwise coloured—regardless of fibre composition or construction.
The standard is technically equivalent to ISO 105-B02:2014 with specific modifications to accommodate Canadian climate conditions and industry practices. It is widely referenced by textile manufacturers, importers, and certification bodies in Canada to ensure product durability and performance when exposed to sunlight during use or display.
Technical Requirements and Test Procedures
Test Principle
Specimens of the textile material are exposed simultaneously to a controlled xenon arc light source and to a series of blue wool reference standards. The test is continued until a specified contrast (typically the change on the grey scale or the fading of a particular blue wool standard) is reached. The colourfastness is then assessed by comparing the change in the specimen with that of the reference standards.
Apparatus and Materials
The following equipment and materials are required:
- Xenon arc fading lamp — Equipped with filters to simulate the spectral distribution of natural daylight (type 2 or type 3 filters as defined in the standard).
- Test chamber — Capable of maintaining specified temperature, humidity, and irradiance levels.
- Blue wool references — A set of eight dyed wool fabrics numbered L1 to L9 (excluding L4) corresponding to lightfastness ratings 1 to 8 (where 8 is the most resistant).
- Grey scales — For assessing change in colour and staining.
- Cardboard or metal mounting panels and opaque masks to create half‑exposed areas.
Preparation of Specimens
Each textile sample is cut to a size of approximately 50 × 100 mm. The specimen is mounted on a backing card, and an opaque cover is placed over half of its length to provide an unexposed reference area. For loose fibres or yarns, a uniform layer is formed on a card. Blue wool standards are cut and mounted in the same manner.
Exposure Conditions
The test is performed under controlled parameters. The table below summarises the standard exposure conditions:
| Parameter | Requirement |
|---|---|
| Irradiance (at 420 nm) | 1.10 ± 0.03 W/(m²·nm) |
| Black‑standard temperature | 47 ± 3 °C (light cycle) |
| Chamber temperature | 45 ± 3 °C (light cycle) |
| Relative humidity | 65 ± 5 % |
| Light/dark cycle | Continuous light (unless otherwise specified) |
| Duration | Until the defined blue wool standard reaches the prescribed fading (e.g., contrast 3 on the grey scale for standard L7) |
Tip: Irradiance and temperature set points should be verified regularly with a calibrated radiometer and a black‑standard thermometer. Inconsistent chamber conditions are the leading cause of non‑reproducible results.
Grading and Evaluation
Assessment Using Blue Wool Reference Standards
After exposure, each specimen is compared with the unexposed portion using the grey scale for change in colour (rating 1 to 5). The colourfastness rating is the number of the highest blue wool standard that shows a similar amount of fading. For example, if the specimen matches the fading of blue wool L5, its lightfastness rating is 5.
The standard defines two exposure endpoints:
- Method 1 (End‑point method): Exposure is terminated when the blue wool standard specified in the product specification has reached a contrast equal to grey scale grade 3.
- Method 2 (Stage method): The specimen is exposed alongside a series of blue wool references for predetermined durations, and the rating is determined by interpolation.
Compliance benefit: Regular use of CAN CGSB 4.2 No. 73.2‑M91 helps manufacturers demonstrate that their products meet Canadian market expectations for fade resistance, reducing returns and building consumer trust.
Warning: Blue wool references are sensitive to humidity and spectral variations. Store them in a cool, dark, dry environment and replace them as recommended by the supplier. Using expired or contaminated references will invalidate test results.
Compliance and Quality Assurance Notes
- Laboratory accreditation: Testing to CAN CGSB 4.2 No. 73.2‑M91 should be performed by laboratories accredited to ISO/IEC 17025 or recognized by the Standards Council of Canada (SCC).
- Reaffirmation status: Originally published in 1991 (M91), the standard was reaffirmed in 2013. The technical content remains current; however, users should verify that no amendments have been issued by CGSB in later years.
- International alignment: The test method is harmonized with ISO 105‑B02, AATCC TM 16.3, and other national standards, facilitating global acceptance of test results.
- Deviations: Canadian climatic conditions (higher UV index in southern latitudes) may justify selection of a stricter performance level (e.g., minimum rating 5 for apparel versus rating 4 for indoor textiles).
Non‑compliance risk: Failing to adhere to the conditioning and exposure requirements of CAN CGSB 4.2 No. 73.2‑M91 can lead to premature fading complaints, product liability issues, and rejection by Canadian retailers.
This technical guide was prepared in 2026. The original standard was published in 1991 and reaffirmed in 2013. Always refer to the latest official version from the Canadian General Standards Board for mandatory compliance.
Q: Is CAN CGSB 4.2 No. 73.2‑M91 identical to ISO 105‑B02?
A: The standards are technically equivalent, but the Canadian version includes specific humidity and temperature tolerances. In most cases, testing to ISO 105‑B02 using the same conditions will satisfy the CGSB requirements, but it is advisable to explicitly request the CGSB method if Canadian compliance is needed.
A: The standards are technically equivalent, but the Canadian version includes specific humidity and temperature tolerances. In most cases, testing to ISO 105‑B02 using the same conditions will satisfy the CGSB requirements, but it is advisable to explicitly request the CGSB method if Canadian compliance is needed.
Q: Which blue wool standards are recommended for general apparel?
A: For most outdoor apparel, a minimum lightfastness rating of 5 is common. This corresponds to blue wool L5. For products intended for heavy sun exposure (e.g., outdoor furniture), a rating of 6 or higher is often specified.
A: For most outdoor apparel, a minimum lightfastness rating of 5 is common. This corresponds to blue wool L5. For products intended for heavy sun exposure (e.g., outdoor furniture), a rating of 6 or higher is often specified.
Q: How often should the xenon arc lamp be replaced?
A: Lamp replacement intervals depend on accumulated hours and manufacturer recommendations, typically between 1500 and 2000 hours of operation. Regular monitoring of irradiance output and spectral distribution is more reliable than fixed schedules.
A: Lamp replacement intervals depend on accumulated hours and manufacturer recommendations, typically between 1500 and 2000 hours of operation. Regular monitoring of irradiance output and spectral distribution is more reliable than fixed schedules.
© 2026 Canadian Standards Advisory — This article is for informational purposes and does not replace the official standard. Always consult the current version of CAN CGSB 4.2 No. 73.2‑M91 for certification purposes.