How is lightfastness measured for textile dyes?

Lightfastness, which refers to a material's ability to resist fading or color change when exposed to light, is measured using a standardized numerical scale.12

Measurement Standards

Lightfastness is assessed on a scale of 1 to 8, where 1 represents the poorest resistance to fading and 8 represents the highest level of performance. This assessment is part of a broader framework of fastness testing used to ensure that textiles meet specific quality requirements for their intended use.1

Organizations and Standardization

The development of these testing methods and standards has been led by several prominent organizations, including:
* The American Association of Textile Chemists and Colorists (AATCC)1
* The Europäisch-Continentale Echtheitsconvention (ECE)1
* The Society of Dyers and Colourists (SDC)1

Efforts to create a unified global system for these evaluations are managed by the International Organization for Standardization (ISO). While lightfastness uses an 8-point scale, fastness to other agents—such as water, bleach, and detergents—is typically measured on a 5-point scale.13