Light fastness to the skin is made to determine how much the sun's rays affect the physical properties of the skin and the permanence of the paint on it, and how long the skin can resist if exposed to sunlight for a long time. In recent years, artificial light such as quartz lamps have been used in light fastness tests. However, the truth is that even if there is an illumination equivalent to daylight, these tests are performed under natural conditions.

A blue scale is used for light fastness assessment studies. Light fastness values ​​vary from one to eight on this scale. The higher the fastness value of the skin, the better the fastness.

The fastness of dyes is not an absolute property. It differs according to certain factors such as water, sweat, light and the material to which it is applied. In this respect, the choice of dyestuff to be applied to the skin is important in terms of its permanence and resistance to light.

Tests are carried out by laboratories accredited from domestic and foreign accreditation organizations to determine the sensitivity of the skin to light within the scope of specific tests. In these tests, national and international standards are taken into consideration. The standards for determining light fastness to the skin are as follows:

• IUF 402 Color fastness to leather light: Xenon lamp Color fastness of leather to light: Xenon lamp
• TS EN ISO 105-B02 Textile - Color fastness tests - Part B02: Determination of color fastness to artificial light - Xenon arc fading lamp test

These standards include a method for determining the color effect of all textile products, including leather. This method evaluates the color fastness of textile products of all kinds and structures against artificial light sources of the same value as natural daylight. This method is also applied to bleached or optically polished textile products.