The filaments are coated with oxides of barium and strontium, resulting in thermionic emission which can ionize the argon gas inside the tube. This results in a high current to flow through the filaments F1 and F2 and the choke circuit. In a while, the bimetallic strip bends and short circuits the starter terminals. This argon gas ionized and a glow appears inside the starter switch, which heats up the bimetallic strip carrying a moving contact.
The starter switch is filled with argon gas. When the circuit is energized, nearly full supply voltage appears across the starter terminals due to low resistance of the filaments and a negligible current flows through the choke. The circuit diagram of a fluorescent lamp is shown Figure-2. The lamp filament is connected to a starter switch which is a small cathode glow lamp with bimetallic strip at the electrodes. A choke is also connected in series with the tube filament that provides a voltage impulse for starting the fluorescent lamp and once the lamp is started, it acts as a ballast. The electrodes are of spiral form, made of tungsten and coated with an electron emitting material. The tube is filled with a small amount of mercury vapor and a small amount of argon gas.Īt both ends of the tube, the electrodes are attached.
Thus, due to low pressure, the lamp is made in the form of a long tube whose inside walls are coated with some phosphor. The fluorescent lamp is a low pressure mercury vapor lamp. The basic construction of a fluorescent tube lamp is shown in Figure-1.
When an electric current is passed through the fluorescent tube, it excites the mercury vapor which produces UV rays that then causes a phosphor coating on the inside of the lamp to glow. A fluorescent lamp, also called fluorescent tube, is a low pressure mercury vapor gas-discharge lamp that works on the principle of fluorescence to emit visible light.
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