Double-wavelength UV excitation fiber: The fibers are usually used to be mixed in the paper pulp to makethe security paper. They are colorless (means white) under the natural light so that they are invisible in the white paper under the natural light, while they can fluoresce(such as red) under the long-wave ultraviolet light and fluoresce(another color such as green) under the short-wave ultraviolet light. The fibers can be extracted from the paper by using the needle. l