How do they test for light fastness?

Light fastness testing is performed to assess the resistance of materials, such as textiles, paints, dyes, and pigments, to fading or color change when exposed to light. There are several methods used to test light fastness, and I will provide an overview of two commonly used methods:

1. Xenon Arc Testing (ASTM G155, ISO 105-B02): This method involves exposing the test specimen to artificial light generated by a xenon arc lamp that simulates natural sunlight. The specimen is mounted in a sample holder and subjected to controlled conditions of temperature, humidity, and light intensity. The exposure duration varies depending on the intended application of the material. Throughout the test, color changes or fading are periodically assessed using color measurement instruments or visual observation. The results are then compared to a control specimen to determine the material's light fastness rating.

2. Fadeometer Testing (ASTM D6386): In this method, the test specimen is exposed to a controlled light source, such as a carbon-arc or mercury-vapor lamp, which emits specific wavelengths of light. The specimen is usually mounted on a rotating drum and undergoes continuous exposure to light. The light intensity, temperature, and humidity can be adjusted to simulate various environmental conditions. Color changes and fading are measured periodically using spectrophotometers or colorimeters. The results are evaluated against a specified rating scale or compared to a control sample to determine the light fastness properties.

Both xenon arc testing and fadeometer testing simulate light exposure over an extended period, allowing for accelerated assessment of a material's light fastness. These tests help manufacturers and researchers understand how different materials may react to prolonged exposure to light and allow them to develop products with improved light stability and durability.

It's important to note that specific industries or regulations may have their own standardized light fastness testing methods and criteria. When conducting light fastness testing, it is crucial to follow the prescribed standards and procedures to obtain reliable and comparable results.