Correlation of Accelerated Lightfastness Testing of Paper Products with Actual Storeroom Exposure

The lightfastness of printed and dyed paper products in a simulated storeroom was correlated to the results found in four accelerated fade instruments. The best correlation based on Spearman rank correlation coefficients using color difference measurements was with the HPUV Indoor Actinic Exposure System. However overall instrument-storeroom correlations were only fair to poor. Correlations between instruments with different sources were generally good and were much better than the instrument-storeroom correlations. This suggests that a good spectral match of irradiating sources, although necessary, is not sufficient to insure good accelerating aging correlations. Secondary factors in the instruments' testing significantly changed the rank orders found in the storeroom. Analysis of samples fade paths in CIELAB color space showed several examples where the instruments' paths diverged from the storeroom path.