How to Run the Humidity Control in ISO 105-B02
Blog
Last Updated 2026
Understanding effective humidity and how it impacts textile lightfastness testing is critical for meeting the requirements of ISO 105-B02 Textiles — Tests for colour fastness Part B02: Colour fastness to artificial light: Xenon arc fading lamp test. Because this test was developed prior to the development of today's modern weathering chambers, which can precisely control humidity, it relies on reference materials to ensure consistency.
What is Effective Humidity?
Unlike relative humidity (referenced in numerous test methods), effective humidity is a term specific to ISO 105-B02. It describes the humidity performance within a test chamber by measuring how it impacts a specific reference material. This fabric is a piece of wool dyed with a red azoic dye that is highly sensitive to moisture. As the humidity in a chamber increases, the lightfastness of this fabric decreases.
How to Perform the Humidity Control Test
To verify that your tester is meeting the required effective humidity for your chosen cycle, follow these steps:
- Prepare Reference Materials: Use the humidity-test control red azoic dye fabric alongside the standard blue wool references.
- Run the Exposure: Operate the test cycle until the humidity-test control fabric reaches a specific level of fading—typically a contrast equal to Grey Scale Grade 4.
- Assess Performance: Once that fade level is reached, compare the performance of the control fabric against the specified blue wool references for each exposure cycle to determine if the chamber has met the "effective humidity" requirements.
Exposure Cycles and Requirements
ISO 105-B02 includes different cycles to replicate various global climates. Each has its own effective humidity target:
Exposure Cycle | Climate Replicated | Effective Humidity Target | Verification Requirement |
Cycle A1 | Normal / Temperate | ~40% | Red control fades same as Blue Wool 5 |
Cycle A2 | Extreme Low / Dry | <15% | Red control fades same as Blue Wool 6 |
Cycle A3 | Extreme High / Semi-tropical | ~85% | Red control fades same as Blue Wool 3 |
Why This Matters for Your Testing Program
While modern testers (like the Q-SUN xenon test chambers) offer precise relative humidity (RH) control, ISO 105-B02 still requires the use of reference-based methods to ensure data remains comparable across decades of testing. Although Q-Lab's initial recommendation is to use an RH setpoint of 40%, many users find that setting their modern tester to a target RH of 50-55% is often necessary to achieve the specific 40% "effective humidity" required by Cycle A1. Understanding this distinction is the key to passing your next proficiency test and delivering reliable data to your customers.
Ready to start testing? Contact our team today to get started!
Frequently Asked Questions
Q: What is "Effective Humidity" in ISO 105-B02 testing?
A: Effective humidity is a term unique to ISO 105-B02 that is used to describe the humidity performance of a test chamber based on the fading behavior of a specific reference material—the red azoic dye humidity-test control fabric. Unlike standard relative humidity, it is measured by the moisture-sensitive performance of the test material itself.
Q: What is the humidity-test control fabric?
A: The humidity-test control fabric is a piece of wool dyed with a red azoic dye. It is used as a reference because its lightfastness is highly dependent on the moisture content in the air; as humidity increases, the fabric's resistance to fading decreases.
Q: How do I verify the effective humidity of my test chamber?
A: Verification is performed by exposing the humidity-test control fabric alongside blue wool references until the control fabric reaches a specific level of fading—typically a contrast equal to Grey Scale Grade 4. If the red humidity test control fabric meets the performance of the blue wool reference provided in the table in ISO 105-B02, then the tester meets the standard's requirements.