What Are Fluorescent Light Bulbs Made Out Of?


Florescent light bulbs have become a popular alternative to traditional incandescent light bulbs because of their high efficiency and long life span. Although they are more complex than a traditional bulb, they work on a few basic principles.


  • The body of a fluorescent light bulb is made like any light bulb, using glass. Molten glass is blown and molded into shape using compressed air, creating clear tubes or spirals with two open ends. The glass in florescent lamps is blown very thin, making each bulb extremely light and fragile.


  • Once the glass tube is blown into shape, a white coating of phosphors is applied to the inside walls of the glass. Phosphor salts are able to convert UV light into visible light, a process that allows the UV light created by electrically exited mercury vapor to power and light up the bulb.

Mercury & Other Gasses

  • Once the glass tubes are coated internally with a thin layer of phosphors, one end is sealed with a cathode and cap, while the other is affixed with a small glass tube. A vacuum evacuates all air from the tube, a drop of mercury is injected into the tube, along with noble gasses like argon, xenon and neon. The tube is then sealed with another cathode and cap.


  • The basic electronics of a florescent light are the cathodes capping each end of the bulb. Each cathode is a tungsten coil coated with barium, strontium and calcium oxides, which then conduct electricity into the bulb, exciting the gasses contained within. Each cathode releases free electrons into the bulb creating plasma, or an electrically excited state of gas. Florescent lights also require a power supply to regulate the current flowing into each bulb. Compact florescent lights (CFL's) have a ballast contained within the base of the bulb, while light fixtures using florescent tube lights require a separate ballast.

Put Them all Together

  • When a florescent light is turned on, current flows into each cathode, releasing a storm of free electrons. Free electrons collide with noble gasses within the bulb, ionizing them, creating plasma. The bombardment of free electrons by the cathodes and plasma also excite the mercury vapor, causing its electrons to jump between energy levels and release UV light. The UV light energizes and excites the phosphor coating lining the bulb, causing its electrons to jump between energy levels, thereby releasing visible light.

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