White, the symbol of peace and tranquility, is one of the most popular apparently 'achromatic' dyestuff used in textiles. Generally most of the formal wares and summer cool clothing are White or light pastel shades augmented with Whites. Such Whites obtained by the Optical Brightening Agents (OBA), also called as 'colorless dyes' are considered to be the second most widely used dyes on cellulosic material after Black. The other major non textile usage of OBA's is in Paper and Detergent industries. Many researchers have published abundant and detailed information on chemistry, principle and mechanism of Optical brightening agents. Generally, the OBA's are organic compounds possessing property of fluorescence i.e. absorb light of shorter wave-length (invisible ultraviolet rays in 300-400 nm range), convert it in to Bluish violet light and emit it at longer wavelengths (430-460 nm range of visible spectrum). Thus, the resultant OBA treated textile material emits more than the total amount of light that falls on it, giving brilliant white effect. The average reflectance value measured from the complete range of visible spectrum (400 to 700nm) is called Whiteness and it is commonly measured in terms of Whiteness Index based on CIE, Ganz, Burger, Hunter, etc. formulae.
Source: Technical Service, Atul Ltd (Colors Division), Atul - Valsad, Gujarat, India