Light Fastness
Light fastness is a colorfastness test item that indicates how resistant textile or product colors are to fading or discoloration when exposed to light such as sunlight.
Contents5 sections
Definition and Overview
Light fastness indicates resistance to the phenomenon in which dyes or pigments change color due to exposure to light. It is a type of colorfastness, and the evaluation results are used to select textiles and manage product quality in order to confirm color retention.
Changes caused by light include not only fading, where color becomes lighter, but also discoloration, where the hue changes. Evaluation is performed by comparing a specimen exposed to light under specified conditions with a reference, and in general, a higher grade indicates that color change due to light is less likely to occur.
Effects on Appearance and Function
When light fastness is insufficient, the original color tone may change partially or overall when worn, displayed, or stored in a sunny place. Whether the color is dark, vivid, or light, the way changes appear and how noticeable they are differs by color.
This does not directly indicate textile thickness, hand, elasticity, or sewability. However, because fading affects the product appearance and color matching, it is necessary to pay attention to differences in color change among materials such as switching parts, outer fabric and accessories, and printed areas.
Main Applications and Checking Situations
Checking light fastness is especially important for clothing used often outdoors, outerwear exposed to sunlight, sportswear, uniforms, hats, and bags. It is also checked according to the application for interior uses such as curtains and cushions that are used for long periods near windows.
It is not a requirement only for spring and summer items or light-colored products; its importance changes depending on the wearing region, storage environment, and sales format. Since long-term display under store lighting and displays can also cause appearance changes, expected usage conditions are organized during planning.
Selection and Handling Notes
When selecting textile, do not determine suitability based only on the grade of light fastness; also check the application, expected hours of sunlight exposure, color, and whether there is printing or post-processing. Even with the same color name, results may differ depending on the dye, processing, and lot, so check test results or actual samples as needed.
Light fastness is not an item that indicates shrinkage or color loss due to washing. Compared with washing fastness, rubbing fastness, and perspiration fastness, the factors and test conditions for color change and transfer are different. During sewing, also check whether color differences between the outer fabric, tape, interfacing, and sewing thread will remain noticeable over time.
During storage, the basic rule is to avoid environments where direct sunlight or strong lighting continues for long periods. Since light may still affect products even through transparent packaging materials, consider storage and display methods according to the product characteristics, and reflect them in care labels and sales guidance.
Frequently Asked Questions
If light fastness is high, will the color not fade outdoors?
The higher the light fastness, the less likely light-induced fading or discoloration is to occur, but it does not mean fading can be completely prevented. The strength of sunlight, exposure time, humidity, dyeing method, and storage conditions all have an effect. It is important to assume the actual usage environment and set the required performance accordingly.
What is the difference between light fastness and washing fastness?
Light fastness checks resistance to fading or discoloration caused by light such as sunlight, while washing fastness checks resistance to fading or discoloration during washing and to color transfer to other items. Both are quality items related to color, but because the contributing factors and evaluation methods differ, both should be checked according to the application.
