Perspiration light fastness and light fastness are two different tests used to measure the resistance of a fabric’s colors to fading.

Light fastness is a measure of a fabric’s resistance to fading when exposed to light. It is a measure of the degree to which the fabric’s colors change after exposure to light over a specified period of time. This test helps to determine the fabric’s overall resistance to fading, and is an important factor in selecting appropriate dyes and processing methods.

On the other hand, perspiration light fastness is a test of a fabric’s light fastness after exposing it to sweat conditions, which simulates the effects of body fluids on the fabric. This test helps to determine the resistance of the fabric’s colors to fading caused by sweat exposure, which can occur during normal wear and usage.

The results of both tests are used to determine a rating for the fabric, with higher ratings indicating greater resistance to fading. When choosing dyes and processing methods, it is important to consider both light fastness and perspiration light fastness to ensure that the finished product will have good colorfastness over time.