Variations in Assessment of Light Fastness and in Rates of Fading and Spacing of the Blue Standards

Variations in visual assessments of fastness to light, and in rates of fading and spacing of the blue light‐fastness standards, are discussed. Comparisons are made of the effect of sample size, seasonal variations, and visual and colorimetric assessments. Assessment varies more with observer than with pattern size. Standards above 3 are spaced irregularly. The average spacing of Standards 1–6 is by a factor greater than 2. Luminous flux and radiant energy requirements for fading calculated in different ways differ seriously. Although colorimetric estimates of fading based on graphical transformations of MacAdam ellipses agree fairly well with visual assessment, the correlation differs from colour to colour.