Monday, September 22, 2014
Is anything truly non-fluorescent?
In the Paper Industry, we often measure fluorescence as the fluorescent component of brightness. The instrument makes a brightness measurement which includes the effect of optical brighteners by using a calibrated UV Level (UV-included). The instrument then makes a brightness measurement with a UV-cutoff filter in place to eliminate the effect of the optical brighteners (UV-excluded). The resulting difference (UV-included minus UV-excluded) is identified as the Fluorescent Component of brightness. Things that can effect this result are the raw material, processing that may physically alter the raw material (e.g. refining) and additives to the sample.
Generally, samples with a fluorescent component of 0.25 or less are considered to contain no optical brighteners. This value is used in some specifications to: 1) prevent optical brightening agents from coming into contact with food, or 2) maintain a contrast between substrate and inks. Fluorescent component can measure above 0.00, but less than 0.25 due to intrinsic fluorescence (from virgin fibers) and due to limitations in the repeatability and reproducibility of the instrumentation.
Therefore, it is common for samples to have a fluorescent component above zero, and still be classified as non-fluorescent.