Optical brighteners are additives used by paper manufacturers to make a paper look whiter and brighter.

To make a paper look whiter, it is important to add substances to the paper that shift the invisible ultraviolet spectrum between 320 and 400 nanometers into the visible range from 400 nanometers. This makes the paper bluer or fluoresces in areas that are just visible to the human eye. While our eyes perceive this as a brighter, bluish white, a colorimeter only sees a different blue. Thus, the colour measurements are slightly falsified by the optical brighteners, the created profiles could be yellowish, as the measuring device tries to correct the blueness of the paper.

Many “high white” papers have optical brighteners in them. Partially, the brightening effect weakens over a relatively short period of several years, thus the wisdom of the paper decreases.

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