Definition
Lightfastness describes the resistance of dyes, print pastes, and finishing agents on textiles to the bleaching and degrading effects of light, particularly ultraviolet and visible radiation. Poor lightfastness occurs when light energy breaks chemical bonds within the dye molecule, causing color change or complete fading. Lightfastness is rated on a standardized scale on which high values indicate minimal change and therefore good resistance to light. It must be distinguished from wet rubbing fastness or wash fastness, as it describes exclusively the response to radiation exposure.
Use in the textile industry
Lightfastness is particularly relevant for textiles subject to prolonged light exposure, such as upholstery fabrics, curtains, awning fabrics, outdoor workwear, and sportswear. When selecting dyes for such applications, preference is given to dyes that are structurally more stable against photodegradation, including certain reactive, vat, or disperse dyes. In addition, UV absorbers and light stabilizers can be applied as a finish to improve the overall lightfastness of the finished article.
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