2 – LIGHT FASTNESS:

There is large variation in the light fastness rating of these compounds when applied to celluosic and protein fibers their light fastness range 1 to 2, and in some instance may reach 3. It should be pointed out that this poor light fastness is not too important in the cause of cellulosic’s, since any loss of OBAs effect due to sunlight will be replaced in subsequent laundering with domestic detergent. Fluorescent brighteners on xylon can reach a light fastness rating 4 with selected OBAs, a rating as high as 7 for polyesters, and in this class of acrylic fibers a light fastness of about 4 – 5.
The poor overall light fastness of fluorescent brighteners is due to their continuous absorption & emission of light which result in their chemical degradation.