Fluorescent Lights : Fluorescent tubes, and their smaller cousins compact fluorescent lights (CFLs), work in a strikingly different way to LEDs. Fluorescent tubes are made up of a long glass tube with metal fittings on each end where electricity is passed into them. Inside the glass tube is a small amount of magnesium and an inert gas (a gas which does not normally react to stimulation such as heat or electricity), usually argon. The inside of the glass is coated in a phosphorous powder. When electricity is passed into the metal caps at each end, it excites the magnesium inside the tube. Magnesium atoms then release energy in the form of ultraviolet light, which is invisible to the naked eye. When the ultraviolet light hits the phosphorous coating, the phosphorous begins to glow, creating light.