Special filament reacts with ultraviolet light.  It's a filament that emits light when irradiated with ultraviolt light.  The printed model emits light under UV light because its internal special material reacts to the UV light.  There are three possible colors "red""blue""green".  Because the light emitting material is a complex sructure of organic molecule and absorbs light energy efficiently, it emits strongly under UV light (380-400nm).  Utilizing this characteristic, it is possible to add anti-counterfeit function and improve product design.