Optical brighteners, Optical brightening agents,or fluorescent whitening agents are dyes that absorb light in the UV and violet region (usually 340-370nm) of the electromagnetic spectrum, and reemit light in the blue region (typically 420-470). Fluorescent activity is a short-term or rapid emission response, unlike phosphorescence, which is a delayed emission. These additives are often used to enhance the appearance of color of fabric, paper and plastics causing a whitening effect, making material look less yellow by increasing overall amount of blue light reflected.

　　Optical brighteners, Optical brightening agents,or fluorescent whitening agents absorbs near-ultraviolet light (wavelength 300-400 nm) that is invisible to the human eye, and then emits blue-violet fluorescence (wavelength of about 420-480 nm) visible to the human eye. The optical properties of fluorescent whitening agents are used to improve the whiteness and gloss of textiles, paper, plastics and the like. There are many varieties of fluorescent whitening agents, and more than 3,000 brand names have been used. The fluorescent whitening agents that have been produced have 15 basic structural types and nearly 400 different structural compounds. However, most of them are no longer produced.

　　Optical brighteners, Optical brightening agents, or fluorescent whitening agents are widely used in industries such as textiles, paper, plastics, and synthetic detergents because they significantly increase the whiteness and gloss of the substrate (substrate). Fluorescent whitening agents can also be considered as a white dye, or a white fluorescent dye, which is administered to the visual organs by fluorescence to increase the perception of whiteness. Fluorescence is a phenomenon of photoluminescence. Many substances that absorb light do not necessarily fluoresce; compounds that fluoresce may not be used as fluorescent whitening agents.