- Fluorescent Lamp Definition: A fluorescent lamp is defined as a light source that uses low-pressure mercury vapor and phosphor coating to produce visible light.
- Components: The construction of a fluorescent lamp includes a lime glass tube, mercury, argon gas, a phosphor coating, electrode coils, and aluminum caps.
- Electrode Function: The electrodes, acting as both anode and cathode, are coated with oxides to emit free electrons and are protected to reduce wattage loss.
- Gas and Pressure: The lamp contains low-pressure mercury vapor and argon gas, with pressure inside the lamp at around 0.3% of environmental pressure.
- Shapes and Sizes: Fluorescent lamps are available in straight, U-shaped, and spiral forms to suit various lighting applications.
A fluorescent tube light is a low-pressure mercury-vapour lamp. Visible light comes from a phosphor coating on the glass. The tube itself is built from
- a lime glass tube
- drop of mercury
- argon gas
- phosphor coating
- electrode coils
- mounting assemblies
- aluminum cap
A complete lamp circuit also needs two bases and either an electromagnetic ballast (choke) plus a starter, or an electronic ballast.
- The electrode mount assemblies are at both the ends of lamp tube.
- This electrode mounting assembly is almost similar to the stem press unit in the incandescent lamps.
- The electrode is similar to the incandescent lamp filament.
- The filaments of electrodes play both roles as anode and cathode.
- Small plates are attached to the filament to protect the electron bombardment and reduce the wattage loss at both ends.
- The filament is coated in a mixture of barium, strontium and calcium carbonate. During manufacture it is baked to oxides so it emits electrons at a lower temperature.
- Liquid mercury is provided inside the lamp bulb.
- Phosphor coating is used on inner wall of the bulb tube.
- At a certain pressure argon gas is filled up inside the tube.
- Two pins at each end are taken out of the lamp body through the cap.
The figure of an electrode is shown below.
The tube holds low-pressure mercury vapour and argon. The fill is about 0.3% of atmospheric pressure. The inner wall is coated with metallic and rare-earth phosphor salts. The electrodes are coiled tungsten coated with barium, strontium and calcium oxides so they emit at a lower temperature. A linear Fluorescent lamp is typically 600 mm to 1200 mm long (2 ft to 4 ft), not 100 mm. Circular, U-shaped and spiral tubes are used where a short lamp must still give a long arc.
To construct a fluorescent tube light you start with a lime-glass tube, a drop of mercury, argon, a phosphor coat and the electrode mounts. The finished lamp still needs two bases and a ballast. The electrode mount is like the stem press of an incandescent lamp. The coils act as anode and cathode. Small plates limit electron bombardment and end-loss watts.
The electrode looks like an incandescent filament but is dipped in barium, strontium and calcium carbonate and baked to oxide so it emits electrons freely.
