Light fastness refers to the performance of UV flexo printing ink that its color does not fade under the action of sunlight. To master the lightfastness of various UV flexo inks, you must first understand the lightfastness level of each UV flexo ink, which is divided according to the BWS international standard. The BWS consists of 8 levels, from the lowest level 1 to the highest level 8. All UV flexo inks must be tested for lightfastness in a specific laboratory. To ensure that the printed matter can maintain bright colors for a long time.