There are many factors affecting the wavelengths and intensities of ultraviolet (UV) rays that reach the Earth through the atmosphere.

The main protective factor is the ozone layer.

The intensity and wavelength distribution of ultraviolet rays are influenced by the daily and seasonal position of the sun and the action taken. At noon the sun is at the top and the rays descending to the earth pass through a shorter layer of air. As such, the rate of filtering ultraviolet rays by the ozone layer is very low. In contrast, when the sun is low, the sun's rays pass through a thicker layer of air in the morning and noon. In this case, the rate of filtration of ultraviolet rays by the ozone layer is very high.

Fossil fuels are the leading factors that weaken the ozone layer. Fossil fuels, when burned, release large amounts of nitrogen and sulfur oxides into the air. In this way, oxidation and hydrolysis can be combined to degrade especially textile materials. Acids that occur when these gases react with moisture in the air accelerate this degradation.

The yarn is extremely sensitive to these disturbing effects. This progressive effect on the yarns that form the basis of the fabric occurs in the following ways:

• Yarn becomes more perishable
• Wear resistance of the fabric decreases
• Sewing thread starts to lose color

In textile industry, many additives used in finishing processes of fabrics and aggravating this deterioration process are used. These additives, which absorb ultraviolet rays, are much more effective if added during spinning of the raw yarn. However, if added later, for example during dyeing operations, they can be transferred to other components after sewing. In this case the effects are reduced.

The quality of dyes used in dyeing yarns is an important point in reducing the effects of ultraviolet rays. The dyes serve as photostabilizers or photocatalysts. Quality dyes can provide a high degree of sensitivity to ultraviolet rays.

The shorter the wavelengths of ultraviolet rays, the higher the radiation energy that disrupts the sewing thread. Therefore, the following conditions are taken into consideration when performing UV resistance tests of yarns: wavelength, intensity, humidity and temperature values ​​of the air and duration of action of ultraviolet radiation.

Nowadays, controlled production processes are applied in the textile sector and a number of UV blocking chemicals and high quality dyes are used during production. In this way, the strength of the yarn and thus the fabric's resistance to ultraviolet radiation is increased, while products with high color fastness are produced.

Ultraviolet resistance tests of yarns and fabrics in authorized laboratories are carried out on the basis of the legal regulations in force and the standards published by domestic and foreign organizations. These tests generally use wavelengths between the 300 nanometer and the 400 nanometer. If the wavelength is further reduced, the intensity of the test increases.

UV Resistance and Aging tests as a process accelerated sun and space UVA, UVB, UVC lights 10 year, 5 year, 2 year by a certain process calculation by exposure to UV light and after this process, the test results are reported by reporting the observations.

In short, UV rays make physical and chemical changes in sewing threads. These changes occur when the absorbed energy breaks down the polymer chain and the thread loses resistance. On the other hand, the dye molecules on the yarn are broken and the color of the sewing thread begins to fade.

Textile products may have higher UV protection factors than the most powerful protective creams for human skin. However, the requirements for sun protection must be met. The UV standard 801 was developed by the Hohenstein Institute, which focuses on the testing and certification of textile products. In addition, the main standards taken into consideration in the tests are:

• TS EN 13758-1 Textile - UV protection properties of the sun - Part 1: Test method for garment fabrics
• TS EN 13758-2 ... Section 2: Classification and labeling of garments