Neon Lamp Diagram Working Advantages Disadvantages and Applications

Neon Lamp
Principle : "Electrons are emitted from cathode by subjecting the surface of the cathode to very high electric stress so that electrons are forcibly ejected from orbits of atoms against nuclear centrifugal force"
Construction and Working :
  • It has two closely spaced electrodes sealed within a soft glass envelope containing neon, at pressure of 8 torr ( 1 torr = 133.322 Pascal ), ( 1 torr = 1 mm of Hg ).
  • In these, cathodes are heated for emission of electrons and so they are said to have cold cathode but requires very high voltage depending upon distance between electrodes.
  • To built up electric stress i.e. to discharge neon gas starting voltage of about 1.5 to 2 times of the normal running voltage.
  • Electric field strength near cathode is very high and ions under the influence of stray field will gain lot of momentum which will cause cathode sputtering or disintegration.
  • In a closely spaced electrode system, where the negative glow emits light, a series resistance limits the lamp current, the discharge source having a negative flow characteristic.
  • Too low a current will give flickering of the discharge and a high current will give a bright stable discharge, but life will be shorter and blackening of the envelope will occur. Lamp current is therefore specified to identify a standard or high brightness lamp being less than 1 mA or upto about 2.5 mA respectively.
  • If A.C. voltage is applied, each electrodes will turn + ve and - ve alternatively continuous glow is achieved.
  • Thus such cold cathode lamps are suitable for high operating voltage and low current.
Advantages :
  1. It has instant glow.
  2. Available in miniature configuration.
  3. Wide operating range.
  4. Low power consumption.
  5. Cheap in cost.
Disadvantages :
  1. Low light output for given input power.
  2. Small range of colour spectrum.
Applications :
  • It is used as indicator source as unit cost is low.
  • Display applications, letters, numericals.
  • Simulation of candle flame in flickering lamp.
  • Red light for hazardous warning beacons on tall structures.

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