In general, light fastness for reactive dyed cotton fabrics can range from good to poor, depending on the type and amount of reactive dye used, the fiber content of the fabric, and the conditions under which the fabric is exposed to light.

Lighter shades, such as pastel colors, are typically more susceptible to light fastness failures in reactive dyed cotton fabrics compared to darker shades. This is because lighter shades are often achieved using a lower concentration of reactive dye, which can be less stable when exposed to light. In particular, blue shades are more prone to light fastness failures, followed by red and then yellow.

It is also important to note that the light fastness of a reactive dyed cotton fabric can also be influenced by other factors such as the type of light source, the intensity of the light, and the duration of the exposure. For example, exposure to sunlight or artificial light sources with high levels of ultraviolet (UV) light can have a more significant impact on the light fastness of reactive dyed cotton fabrics compared to exposure to indoor lighting.

To minimize the risk of light fastness failures in reactive dyed cotton fabrics, it is crucial to select dyes and dye concentrations that are specifically formulated for high light fastness and to store and use the fabric under conditions that minimize exposure to light. By understanding these factors and taking the necessary precautions, you can help to ensure that your reactive dyed cotton fabrics maintain their color and vibrancy over time.