Light fastness is the capacity of a substance to withstand fading, discolour or weakening under the exposure of light, especially ultraviolet. There is an abundance of products that are regularly exposed to sunlight or artificial lighting in the course of use, storage, and display. The supplies are subject to premature aesthetic or functional disintegration without proper evaluation. Light fastness tests provide a standard procedure for studying the reaction of dyes, pigments, and polymers to light over time. Knowing light induced degradation, manufacturers are able to choose appropriate materials, enhance formulations, and also guarantee longevity of their products during their use in the real world.
Principle and Methodology
The light fastness testing principle is based on the idea of exposing a test sample to a controlled light source that imitates the sun or certain lighting conditions. The sample is placed together with the reference materials and subjected to a specific time under controlled temperature and humidity. The spectral distribution of natural light is generally reproduced using a xenon arc lamp or a fluorescent UV lamp. The specimen is then visually/instrumentally assessed after exposure to the color, shade change or physical properties. The extent of fading is matched with the standardized scales or reference standards to determine a light fastness rating.
