Reference Material
Fluorescent artifacts with a known response provide a benchmark for adjusting the ultraviolet energy in a spectrophotometer. An ultraviolet calibration standard usually consists of a stable plastic or paper substrate treated with a specific amount of whitening agent. By measuring this reference, the instrument software can tune the intensity of the ultraviolet flash to match a standardized illuminant.
This process ensures that the effect of optical brighteners is measured consistently across different devices.
Adjustment Procedure
Fluorescence occurs when a material absorbs invisible radiation and emits it as visible light, making the paper appear whiter. Because the ultraviolet output of lamps varies over time, regular adjustment against a master reference is required to maintain accuracy. The instrument measures the standard and compares the result to the values assigned by a national laboratory or the manufacturer.
If the measured fluorescence is too low, the software increases the numerical weighting of the UV portion of the scan.
Measuring Accuracy
Durability of these standards is limited because the fluorescent molecules degrade when exposed to light or heat. They must be stored in light-tight containers and replaced annually to prevent drift. Using an expired or dirty standard leads to incorrect brightness readings.
