Studies on the Instrumental Method for Assessing the Light Fastness of Colored Materials

Part 1: A proposal of the Instrumental Evaluating Equation on Light Fastness

Abstract

The instrumental method for assessing the light fastness of colored materials was investigated by analyzing the color change of the wool blue standard specimens by exposure to carbon-arc light.
The following equation was obtained from the relation between exposure time to light and the color change indices Nc^# of the wool blue standard specimens.
N_L=ln { (5.5-Nc^#) / (F_L×T^1/n) } / (ln K_L)
where, N_L: light fastness value in accordance with the blue standard numbers
Nc^#: the color change index assessed in accordance with the gray scale rating
F_L: criterion constant of assessment of light fastness
T: exposured time in hours
n: power number determined with K_L
K_L: light exposure time constant
This method is expected to supersede the present subjective visual method for assessing the light fastness.