Ultraviolet
Light with a wavelength just shorter than violet, invisible to humans but seen by many animals.
Also: UV, black light
Ultraviolet lies just beyond the violet end of the visible spectrum. We cannot see it, but bees, many birds and some fish can, and flowers often carry ultraviolet patterns that guide insects to nectar. For colour, ultraviolet matters in two ways. It makes fluorescent materials glow. And it is the main cause of fading: its energy breaks down dyes and pigments over time, which is why museums filter it from their lighting and keep textiles and watercolours in dim rooms.