The lightfastness of pigments refers to the resistance of pigments under light conditions, that is, whether the pigments will change color, fade or fade after receiving light for a long time. The determination of the light resistance of pigments usually requires a light resistance test.

The following are some common methods used to evaluate the light resistance of pigments:

Xe lamp exposure test: Expose the pigment sample to a Xe light source and expose it for a long time. By observing and comparing the color changes of pigments before and after exposure, the light resistance of pigments can be preliminarily assessed.

Ultraviolet (UV) exposure testing: Pigment samples are exposed to a UV light source, typically using a UV lamp or UV accelerated aging equipment. By controlling the exposure time and intensity, it is possible to simulate the light resistance of the pigment under sunlight or artificial light. By observing the degree of discoloration and fading of the pigment, its light resistance can be assessed.

How to determine the lightfastness of pigments

Natural climate exposure test: the pigment sample is placed in the outdoor exposure of natural climate conditions, through the sun, rain, wind erosion and other natural factors. By continuously observing the color change and fade degree of the pigment, its light resistance in the actual environment can be evaluated.

Photometer measurement: A photometer is used to measure the pigment sample and record the light reflectance or transmittance of the pigment under different lighting conditions. By comparing the measurements, the light resistance of the pigments can be assessed.

The evaluation of light resistance usually requires a long time of testing and observation, and the results may be affected by a variety of factors, such as pigment type, formula, concentration, substrate, etc. Therefore, for pigments in specific application areas, more detailed and rigorous light resistance tests may also be required according to relevant standards and requirements to ensure their stability and durability in practical use.