To evaluate the light fastness of colored materials, two types of blue scale have been used as a standard, i.e., ISO-type blue scale in European countries and AATCC-type blue scale in the United States. The former has also been adopted in the Japanese Industrial Standard.
In this paper, the authors have tried to make clear the coloristic charactor and color changing property of these two types of standard by the light exposure such as a carbon arc, xenon and fluorescent light.
The AATCC-type blue scale was found to give more accurate evaluation than the ISO-type blue scale, because every blue specimen of the AATCC-type blue scale shows a stable changing property in color by the light exposure.
The light fastness value in accordance with the blue scale ratinging was calculated by the following equation.
N
L=ln {5.5-N
c#/ (α×F
L×T
l/n) } ln K
Lwhere, N
L: light fastness value in accordance with the blue scale rating
N
c#: assessment of the color change class corresponding to the gray scale rating
F
L: criterion constant of assessment of light fastness
T: exposure time in hours
n: power number determined with K
LK
L: light exposure time constant
α: light source constant
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