Fluorescence is the ability of an object to absorb energy from the invisible part of the electromagnetic spectrum and then re-emit it in the visible part of the spectrum. When a set piece is painted with "fluorescent" paint and placed under UV light, it absorbs that invisible UV light and re-emits it back in a color of light we can see. Fluorescence happens in real-time, whereas phosphorescence (a specific form of photoluminescence) happens over a period of time. Glow tape is a prime example of a so-called "fluorescent" material that exhibits phosphorescence. A fluorescent light tube is actually a Gaseous Discharge lamp that produces UV "Black light" with some modifications. Electricity passes between electrodes in the lamp causing mercury in the gas in the tube to vibrate and produce invisible UV light. This light is partially contained in the tube by the white coating you see painted inside. Also in the tube is a white powdery substance. This substance called the "phosphor" absorbs the invisible UV rays and re-emits them as white light. Glow Tape is just another object that has the ability to Fluoresce. The best way to charge glow tape is with a light high in UV. So using a "blacklight" or fluorescent light will provide a stronger charge.