Fastness to light of a dye is influenced not only by the chemical constitution of the dye but also by several other factors such as physical state of dye in the substrate, concentration of dye in the fiber, nature of substrate, type of bond between dye and fiber, source of radiation and its intensity, temperature, humidity conditions, presence of foreign substances, atmospheric contaminants and after treatments given to dyed fabrics for improving its performance charachteristics. Inter-relations of these factors are so complex that no general rule can be established to describe their effects on the dyes and different fibers. Studies in light fastness of reactive dyes, when present in different fibers in the reacted form and hydrolyzed unreacted state shows wide reaction. In the case of mixture of reactive dyes, rate of fading of one dye can also depend on the other dye present in a combination.

In recent years, consumers demand high rating in light fastness depending on the end-use of dyed and printed fabrics. Exporter also demands high standard of light fastness.

In order to improve dry light fastness the finishing agent Primafin SUN 1585 has been developed and studies being carried out on dry light fastness of commonly reactive dyes of different classes at very low deptg shade.

Bleached, mercerized, and unfinished poplin cotton fabric was dyed as per method suggested by manufacturer with different classes of reactive dyes at three different depths viz. 1/25th, 1/12th and 1/6th. Dyed fabric was finished with 40 g/l Primafin SUN 1985 by keeping 80% expression and dried at 150⁰C. Unfinished and finished fabrics were exposed to sunlight with blue standards 1-8. At every five hours exposed fabrics were examined along with blue standards and ratings were given (Table 1).

Results of studies indicate that dyed fabric finished with Primafin SUN 1985 showed improvement in light fastness by half a unit for most of the dyes studied. Primafin SUN 1985 is a durable finishing agent for protection against uv component of sunlight and thereby improves the light fastness of dyes. Primafin SUN 1585 has high wash fastness and dry cleaning solvent resistance. Feel and shade of the fabric is not affected on application of Primafin SUN 1585.