 These fluorescent bulbs that you are seeing, the long tubes basically have two electrodes on the sides, the electrodes on the sides. And you pass electric current and that creates an arc between the two electrodes. And that tube is filled with inert gases, inert gases being argon or argon plus krypton mixture, no air in there, just argon plus krypton mixture and you spark. And with a little bit of mercury in there, little bit of mercury in there, when you generate that arc between two electrodes on the two sides of that tube, that arc excites these mercury atoms to a higher state. And then when they are coming back to the ground state, they have to release that excess energy that they absorbed and they release it as non-visible UV light. UV light is not visible. UV light is dangerous. Remember, UV light is what comes out when the mercury atoms are coming back to the ground state. But you know, this tube is coated on the inside wall, is coated with a different material, a special material called phosphorous. And those particles that are coated have a unique ability to absorb this UV light that is released when the mercury atoms are coming to the ground state. And that is absorbed and those phosphorous coating will give out visible light. It absorbs UV light and gives out visible light. So without that phosphorous coating in there, a fluorescent bulb would not work. Fluorescence is absorbing UV light, the phosphorous, and giving out visible light. There's a change of frequency, a change of energy style, and that is called fluorescence. And a bulb that uses this principle is called a fluorescent bulb.