One of the most emphasized fastness values ​​in the textile sector is light fastness. It is a known fact that especially short wavelength rays are stronger in energy and cause the dyes on fabrics to fade after a while.

When determining the light fastness of the fabrics, the fabric samples dyed with dyes whose fastness is known and the fastness value of which are desired to be determined are left in the sunlight for a certain period of time. The fading levels of these dyes on the fabric are then compared to determine which of the fastnesses corresponds.

According to the American test methods, the fastness value is measured by measuring the time to fade. In recent years, artificial lights such as quartz lamps have been used instead of solar rays and these measurements have been made.

A blue scale is used to assess light fastness. The light fastness values ​​on this scale range from 1 to 8. These values ​​mean: 1 = Very little, 2 = Low, 3 = Moderate, 4 = Very good, 5 = Good, 6 = Very good, 7 = Excellent, 8 = Marvelous. The light fastness value is the fading level in the tested fabric sample, whichever one of the standard samples.

It should be noted, however, that both the light fastness measurements and the other fastness measurements, the darkness of the dye in the tested sample has an effect on the results. For example, the fastness of light is better for darker stains than for the same stains. However, in the case of washing fastness measurements, the situation is reversed. Lower fastness values ​​are obtained in dark dyeings.

The fastness of light in textile products to determine the negative effects of daylight on fabrics is determined in accordance with the following standard:

• TS EN ISO 105-B02 Textile - Color fastness tests - Part B02: Determination of color fastness to artificial light - Xenon arc fading lamp test