The fluorescent pigment in acrylic products is completely man-made. Basically, manufactured fluorescent dye is added to largest amounts of resin that is then left to dry before being ground to a fine powder to form fluorescent pigment. This pigment is then added to a standard paint base.
Although fluorescent paints can look somewhat subdued in ordinary daylight, their glowing qualities are brought to life with the use of a black light, also referred to as a UV (ultraviolet) light. These black lights actually emit large amounts of ultraviolet light that cannot be seen by the naked eye, and as they are perceived as "black".
The paint absorbs the ultraviolet light from the bulb and then and re-emits it in visible wavelengths that we see as fluorescent colours.