Ultraviolet light (UV), or UV light, is a powerful type of light with a shorter wavelength than violet light of visible light. When artifacts are exposed to UV light, some materials emit fluorescence, showing different colors and strengths. This helps us check how clean and well-preserved the artifacts are, and whether there are any signs of repairs or changes. If something glows when UV light shines on it, the glow will be called "ultraviolet fluorescence," and this process is called "photoluminescence."