It is known that prolonged exposure to light leads to changes in many colors, especially ultraviolet radiation. Thus, in this case, color fastness to light means the material's resistance to changes in color intensity and tone. Such changes are very undesirable, and not only because they cause a general change in the appearance of the tiles. Over time, depending on the degree of intensity and area of light exposure, multi-color (chromatic) zones are formed. This is especially true when it comes to floor or wall tiles located outside and exposed to constant sunlight.
As a rule, the colors used in the production of ceramic tiles are resistant to exposure to sun and light. However, there are some finishes and chromatic effects, especially on glazed tiles, that are more susceptible to change due to this effect.
Methods for testing tiles for resistance to light are given in the German standard DIN 51094 (Ceramic tiles. Testing of the light fastness and color fastness of ceramic tiles for walls and floors / Ceramic tiles for walls and floors. Determination of color fastness).