Usually refers to the safer, long-wave UV-A (350-400 nm) portion of the spectrum and should not include the more dangerous short-wave UV-B light (250-275 nm); both types can be responsible for yellowing of artificial nail coatings. When all the wavelengths of the visible light spectrum strike your eye at the same time, white is perceived. That is why visible light is sometimes referred to as white light. Technically speaking, white is not a color at all, but rather the combination of all the colors of the visible light spectrum. Ultraviolet light is a form of radiation that is not visible to the human eye. It’s in an invisible part of the “electromagnetic spectrum.” Though some ultraviolet waves from the sun penetrate Earth’s atmosphere, most of them are blocked from entering by various gases like ozone.