What is the difference between light fastness and weather fastness of pigments?

Many coatings that use pigments (or dyes) as colorants need to maintain the stability of the inherent color in their application.

Meaning of light fastness of pigments (What is light fastness of pigments?)

We define the light fastness of a pigment as the quality technical index of a pigment's resistance to sunlight. Of the components of sunlight, the most damaging to a pigment's light fastness is ultraviolet (UV) light. When we discuss the light resistance of a pigment, we are only evaluating the QSI of the pigment's ability to withstand the light environment in the external environment. In fact, it is difficult to give a precise definition of the weather condition. From a certain point of view, a pigment light fastness index that excludes other external environmental factors may help us to give a meaningful and reproducible objective evaluation of the coating's stability in the field.

Meaning of weather fastness of pigments (What is weather fastness of pigments?)

The performance of pigment weather fastness(Pigment weathering) is affected by a variety of external environmental factors, including sunlight, high-energy ultraviolet radiation, temperature, humidity and atmospheric impurities. Pigment weathering (For example, automotive grade mica powder has excellent pigment weathering) can be measured either by outdoor exposure tests or indoors using artificial atmospheric weathering equipment to simulate field conditions. Outdoor exposure tests are usually carried out in specific locations, often in areas with very harsh climatic conditions (intense sunlight, heavily polluted industrial atmospheres, etc.), the most famous outdoor exposure test site being Florida, USA. Test samples will generally be placed in the direction of 5 degrees south after 12 months or longer exposure to outdoor exposure experiments.

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