A fluorescent lamp basically consists of a long glass gas discharge tube. Its inner surface is coated with phosphorous and is filled with an inert gas, generally argon, with a trace of mercury.The tube is then finally sealed at low pressure with two filament electrodes each at its both ends.These electrode filaments are used to preheat the tube and initiate a rapid conduction of electrons between the two end electrodes. The process initially requires a relatively high amount of power.The energy also converts some of the mercury from a liquid to a glass. Electrons then collide with the gaseous mercury atoms, increasing the amount of energy. As electrons return to their original energy level, they begin to release light. However, the light they emit is ultraviolet, and not visible to the naked eye, so another step needs to take place before we can see the light.This is why the tube was coated with phosphorous. Phosphors will give off light when exposed to light. When exposed to the ultraviolet light, the particles emit a white light which we can see.