Evaluating the <scp>ISO</scp> Standards for <scp>UV</scp> ‐Content Adjustment Based on Brightness and Whiteness

ABSTRACT Whiteness and brightness are essential perceptual attributes of paper and packaging, significantly influenced by the UV content of illumination, especially when fluorescent whitening agents (FWAs) or optical brightening agents (OBAs) are present. This study quantitatively evaluates the performance of four ISO standards regarding UV‐content adjustment towards two standardized illuminations: ISO 2470‐1 and ISO 11476 for C, and ISO 2470‐2 and ISO 11475 for D 65 . The study involves two fluorescent IR2 (international reference of level 2) standards, whose total spectral radiant (TSR) factors were measured at National Research Council Canada (NRC). The results indicate that all standardized methods effectively reproduce the assigned TSR factors, despite discrepancies in several fluorescence‐intensive wavelengths. However, systematic differences between the ISO standards suggest non‐interchangeability: UV content adjusted with ISO Brightness is slightly higher than with CIE Whiteness; spectrophotometers adjusted against CIE Whiteness read lower ISO Brightness, and vice versa. These differences are more pronounced for C than D 65 and decrease with lower FWAs content. Given the spectral dependence of assigned values—entire spectrum for CIE Whiteness and blue spectral band for ISO Brightness—ISO Brightness‐based methods (ISO 2470‐1 for C and ISO 2470‐2 for D 65 ) are more straightforward for UV adjustment.