Brightness is an optical property of paper that measures the reflectance/reflectance of blue light with a dominant wavelength of 457 nm. The brightness value of this wavelength is taken to indicate the bleaching quality of the pulp. The pulp is bleached to remove residual "lignin" (the glue that holds the cellulose fibers together) which, if present, gives the paper a cream/yellow appearance. Since lignin absorbs strongly at 457 nm, brightness is measured at this wavelength. Commonly followed testing standards are TAPPI T452, ISO (2469 & 2470) and ASTM methods. This characteristic is an important seller of paper, as lighter papers look more attractive than less bright papers.
