n (optical brighteners, fluorescent bleaches, and optical whiteners) Brightening agents are chemicals used primarily in fibers but also to some extent in molded and extruded products, to overcome yellow casts and to enhance clarity or brightness. In contrast to bluing agents, which act by removing yellow light, the optical brighteners absorb ultraviolet rays and convert their energy into visible blue-violet light. Thus, they cannot be used ion compounds containing UV-absorbing agents. Optical brighteners are used in PVC sheet and film, fluorescent lighting fixtures, vinyl flooring, nylon fishing line, polyethylene bottles, etc. A few examples of optical brighteners are coumarins, naphthotriazolyl stilbenes, benzoxazolyl-, benzimidazolyl-, naphthylimide-, and diaminostilbene disulfonates. (Bart J (2005) Additives in polymers: industrial analysis and applications. Wiley, New York). See Brightener, Optical.