Fluorescent lamps are essentially cylindrical glass tubes that are coated with phosphorus and filled with a noble gas. They also contain a small amount of mercury inside. Conventionally, these lamps are shaped as hollow cylinders, but they can be made of other shapes such as U-shape, circline or long twin tubes.
These lamps work on the phenomenon of fluorescence. These lamps are much more efficient when compared to incandescent lamps and also produce much brighter light. The light produced by these lamps falls in the visible region of the spectrum.
When an electric current is passed through a tube it causes electrons and charged noble gas molecules to move between the two electrodes. Some amount of mercury is vaporized and the electrons and noble gas molecules collide with this vapor.
This collision causes excitation, upon returning to their original states the electrons and molecules release energy in the form of ultraviolet radiation is produced. The phosphor coating absorbs the ultraviolet radiation and converts it into visible radiation.
The spectrum emitted by the lamp is a combination of the light emitted by mercury and the phosphorescent coating. The emitted wavelengths are distributed evenly over the visible range of the spectrum. Different colors of light can be obtained by varying the type of phosphorus.
The fluorescent lamp consists of a glass tube (typically cylindrical) having two electrodes at the ends. The tube is filled with a noble gas and a drop of mercury. The tube is coated with phosphorus on the inside. There is ballast connected to the lamp to control the electric current flow within the tube.
Some of the major areas of application of the fluorescent lamps are listed below:-
- Household lighting
- Stage lighting
- Studio lighting