Fluorescent tubes produce light by the excitation of gas molecules. Fluorescent tubes have a gas mixture containing low-pressure mercury vapor and noble gases like argon, neon, or krypton. The gas inside the tube gets excited by electricity and emits ultraviolet (UV) light. The UV light excites the phosphor coating on the inside of the glass tube, causing it to emit visible light. The gas molecules act as a medium for the transfer of energy between the electrical source and the phosphor coating.