Textile fibres, paper & plastics in raw state possessaesthetically undesirable brownish cast. Reason of it in natural fibres ispresence of natural dyes & pigments & in manmade fibers it isattributable to thermal decomposition. Chemical bleaching can remove yellowishtint still they retain faint, creamy colour. Tinting with optical brighteningagents can compensate residual yellowness. Optical brightening agents are usedin paper, detergent, plastic & cosmetic industries.
Abluing agent absorbs yellow light from the sunlight and emits blue light, whichcombines additively with yellow light of the fabric. The resultant colour ofthe substrate is perceived as greywhite as the total reflectance valuedecreases