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Neon Lamp – Principle, Construction, Working, and Applications
A miniature gas discharge lamp in which the electrical discharge takes place through a mixture of gases containing a large proportion of neon gas is known as neon lamp.
The working principle of the neon lamp is as follows −
“Electrons are emitted from cathode by subjecting the surface of the cathode to very high electric voltage so that the electrons are forcibly ejected from the orbits of the atoms against the nuclear centripetal forces.”
Construction of Neon Lamp
The construction of a typical neon lamp is shown in the figure.
The neon lamp has two closely spaced electrodes, but not touching each other, in the form of thick parallel wire spiral or flat plate sealed within a soft glass envelope. The glass envelope is filled with the neon gas at a pressure of about 8 torr. Also, a series resistance of about 2000 ohms is mounted inside the cap.
Working of Neon Lamp
When a high electric power supply is connected to the neon lamp, the cathode terminal starts emitting the electrons. These electrons get accelerated by the electric field and collide with the neon atoms. On collision, a part of the energy is transferred from the electrons to the neon atoms and the neon atoms get excited. When the excited neon atoms and ions come to their ground state, they give off light.
Some important points about the working of neon lamp are listed below −
In the neon lamps, the cathode is heated for emission of electrons. For this purpose, these require a very high voltage depending upon the distance between the electrodes.
In order to discharge the neon gas, it requires a voltage equal to 1.5 to 2 times of the normal operating voltage.
The strength of electric field near the cathode is very high and the ions under the influence of stray field will gain a lot of momentum which will cause disintegration of the cathode.
A very small lamp current will give flickering of the gas discharge and a high lamp current will give a bright stable discharge, but life will be shorter and blackening of the envelope will occur. Therefore, the lamp current for a standard neon lamp is less than 1 mA or fir a high brightness lamp is up to 2.5 mA.
When AC supply is used, each electrode will turn positive and negative alternatively. Hence, a continuous glow from the lamp is achieved.
Therefore, these types of neon lamps are suitable for high operating voltage and low current applications.
Advantages of Neon Lamps
The primary advantages of the neon lamps are as follows −
The neon lamps are available in miniature configuration.
Neon lamps have instant glow.
Neon lamps are less expensive.
These lamps consume less amount of electricity.
They have long life around 5000 hours.
Disadvantages of Neon Lamps
The main disadvantages of the neon lamps are given as −
Neon lamps have low efficiency.
Neon cannot be used for ordinary lighting purposes like domestic lighting, etc.
Neon lamps have small range of color spectrum.
Applications of Neon Lamps
The applications of neon lamps are given below −
Neon lamps are used as indicators such as red lights for hazardous warnings.
Neon lamps are also used for advertising purposes.
Neon lamps are used in display applications to show letters, numbers, etc.
Neon lamps are used for decorative purposes.
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