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Understanding CAN CGSB 4.175-M91 Part 5 (2013): Textile Colourfastness to Light — Daylight Test Method
A comprehensive guide to the Canadian standard for evaluating the resistance of textile colours to natural daylight exposure
Introduction to CAN CGSB 4.175-M91 Part 5 (2013)
CAN CGSB 4.175-M91 Part 5 (2013) is a Canadian national standard developed by the Canadian General Standards Board (CGSB) that specifies a method for determining the resistance of the colour of textiles to the action of natural daylight. This standard is part of the CGSB 4.175 series of textile test methods and has been reaffirmed in 2013, ensuring alignment with current industry practices and international test methodologies. It is widely referenced in textile quality assurance, especially for apparel, upholstery, and automotive interior fabrics that require reliable colour performance under prolonged exposure to sunlight.
The standard is technically equivalent to ISO 105-B01:1994 (Colour fastness to light: Daylight) and AATCC TM 16 Option 3, facilitating mutual recognition of test results across global supply chains. This article provides a detailed overview of the scope, technical requirements, implementation highlights, and compliance considerations of CAN CGSB 4.175-M91 Part 5.
Scope and Application
CAN CGSB 4.175-M91 Part 5 applies to all textile materials regardless of fibre composition, construction, or end use. The method assesses the colourfastness of textiles when exposed to natural daylight (excluding direct sunlight) under specified conditions of temperature and humidity. The change in colour of the specimen is compared with that of a set of blue wool references (the blue wool scale) also exposed simultaneously.
The standard is applicable to:
- Woven, knitted, and nonwoven fabrics
- Yarns and threads
- Fibres in loose or flocked form
- Finished garments and textile products
It is not intended for tests using artificial light sources (e.g., xenon arc or carbon arc), which are covered by other parts of the CGSB 4.175 series. The method requires outdoor exposure under a controlled natural daylight environment, making it especially relevant for Canadian climatic conditions.
Tip: When selecting the lightfastness scale, ensure that the blue wool references (L2 to L9) are stored in a cool, dark, dry place before use to prevent any premature degradation that could affect test accuracy.
Technical Requirements
Test Principle
A textile specimen and a set of eight blue wool references (L2, L3, L4, L5, L6, L7, L8, L9) representing progressively higher lightfastness levels are simultaneously exposed to natural daylight on an exposure rack. The degree of colour change of the specimen after a given period is evaluated by comparing it to the colour change of the blue wool references. The lightfastness rating is expressed as a number from 1 (very poor) to 8 (outstanding).
Exposure Conditions
The standard defines the exposure site and apparatus specifications to ensure reproducibility. Key parameters include:
| Parameter | Requirement |
|---|---|
| Exposure location | Outdoor rack facing equator at an angle equal to local latitude |
| Rack orientation | South-facing in the Northern Hemisphere |
| Specimen mounting | Cardboard or aluminium backing; specimen must be flat and securely held at edges to avoid shadows |
| Exposure duration | Until the reference L4 (or other specified reference) shows a colour change equivalent to grade 3 on the grey scale |
| Atmospheric protection | Specimens must be protected from rain and direct wind by a transparent cover (e.g., clear glass or UV-transmitting acrylic) |
Furthermore, temperature and humidity conditions must be monitored (but not controlled), and results are only valid if the blue wool references behave consistently with their known properties.
Blue Wool References (Scale)
The blue wool references are cloths dyed with selected dyes of known lightfastness. Each number from 1 to 8 doubles the lightfastness endurance (e.g., L8 is eight times more resistant than L1). In CAN CGSB 4.175-M91 Part 5, references L2 through L9 are used, corresponding to ISO 105-B01 scale. The following table defines the exposure endpoint criteria using the grey scale for assessing change in colour:
| Blue Wool Reference | Grey Scale Rating at Endpoint | Typical Applications |
|---|---|---|
| L2 | Grade 3 | Low lightfastness testing (e.g., disposable textiles) |
| L3 | Grade 3 | General interior fabrics |
| L4 | Grade 3 | Apparel and curtain fabrics (common specification) |
| L5 – L9 | Grade 3 or specified in contract | Automotive interior, outdoor furniture, military textiles |
Warning: The use of a glass cover alters the spectral distribution of daylight. Ensure the glass does not absorb UV radiation below 300 nm, as this would reduce the effective exposure intensity and invalidate the test.
Implementation Highlights
Sample Preparation
Specimens are cut to dimensions of approximately 100 mm × 150 mm. At least two replicates are prepared for each material along different directions (warp and weft) if the fabric is not uniform. The specimens are conditioned at standard atmosphere (20 °C ± 2 °C, 65 % ± 4 % relative humidity) for at least 24 hours before mounting.
The blue wool references must be freshly prepared; they are normally used only once for a single exposure series. The references are cut to the same size as the specimen and masked with an opaque card covering one‑third of their length so that an unexposed reference area remains for comparison.
Exposure and Evaluation
The specimen and blue wool references are arranged side‑by‑side on the rack, and the assembly is exposed to daylight for a period determined by the rate of fading of the references. Typically, the endpoints are: when the L4 reference shows a colour change equal to grey scale grade 3, the L3 will have faded beyond grade 3, and the L2 will be severely faded. The exposure is continued until the L6 reference reaches grade 3 (for higher fastness materials).
After reaching the prescribed endpoint, the colour change of the specimen is rated by visual comparison with the exposed portion of each blue wool reference. The rating is the lowest number of the blue wool reference that shows the same colour change as the specimen (or less). For example, if the specimen’s colour change matches that of L5, the rating is 5.
Best Practice: Use a neutral grey mask with a viewing angle of 45° under a standard daylight source (D65) to evaluate colour change. This reduces variability caused by lighting conditions.
Compliance Notes
CAN CGSB 4.175-M91 Part 5 is widely imbedded in Canadian federal procurement standards for textiles and in commercial specifications where daylight exposure is a critical performance requirement. To claim compliance with this standard, test laboratories must follow every clause strictly, including the requirement for natural daylight without augmentation. Any deviation from the prescribed method (e.g., using artificial lights) must be documented as a modification, and results cannot be labeled as “according to CAN CGSB 4.175-M91 Part 5”.
The standard should be interpreted in conjunction with:
- CGSB 4.2 No. 46-M88 – Colourfastness to Light: Standard Method (guide for artificial light tests)
- ISO 105-A02 – Grey scale for assessing change in colour
- ISO 105-A03 – Grey scale for assessing staining
- AATCC Evaluation Procedure 1 – Gray scale for colour change
Recent updates in technology have not changed the principal method since reaffirmation in 2013, but practitioners should watch for a new edition or amendment that may introduce updated reference materials (e.g., new blue wool lots).
Important: Do not use this standard for testing textiles that are designed for extreme indoor lighting (e.g., stage lighting) because the natural daylight spectrum is different from incandescent or LED spectra. Use ISO 105-B02 (xenon arc) instead.
Frequently Asked Questions
Q: Can CAN CGSB 4.175-M91 Part 5 be replaced by ISO 105-B01?
A: Yes, the methods are equivalent in technical content. However, for commercial specifications that specifically require “CAN CGSB 4.175-M91 Part 5”, the test must be performed in accordance with that standard. Some suppliers may accept a certificate stating compliance with ISO 105-B01 if mutual agreement is reached.
A: Yes, the methods are equivalent in technical content. However, for commercial specifications that specifically require “CAN CGSB 4.175-M91 Part 5”, the test must be performed in accordance with that standard. Some suppliers may accept a certificate stating compliance with ISO 105-B01 if mutual agreement is reached.
Q: What is the significance of the “M91” in the standard number?
A: “M91” indicates that the standard was originally published in 1991 as a metric standard (M), as opposed to earlier versions that used imperial units. The reaffirmation in 2013 confirmed the method remains valid without modification.
A: “M91” indicates that the standard was originally published in 1991 as a metric standard (M), as opposed to earlier versions that used imperial units. The reaffirmation in 2013 confirmed the method remains valid without modification.
Q: Are there any special requirements for testing dark or very light colours?
A: No special requirements, but note that very light colours may require longer exposure times to show perceptible change. Conversely, dark colours may show fading more quickly. The blue wool scale compensates for these differences because it provides a relative measure of fastness.
A: No special requirements, but note that very light colours may require longer exposure times to show perceptible change. Conversely, dark colours may show fading more quickly. The blue wool scale compensates for these differences because it provides a relative measure of fastness.
Q: How long does a typical daylight exposure test take?
A: The duration depends on the geographic location, season, and weather conditions. In Canada, achieving the L4 endpoint can take from a few days (summer in southern Ontario) to several weeks (winter in northern regions). Laboratories typically schedule tests from May to September to ensure consistent solar irradiance.
A: The duration depends on the geographic location, season, and weather conditions. In Canada, achieving the L4 endpoint can take from a few days (summer in southern Ontario) to several weeks (winter in northern regions). Laboratories typically schedule tests from May to September to ensure consistent solar irradiance.