Question

Let you compare gas discharges under high and low pressure and describe processes that determine each kind of discharge.

Answer 1

Gas discharges are used for variety of lighting application and cover wide range of plasma parameters. Gases begins to conduct electricity at low pressure because at low pressure gases turn to plasma, colliding electrons can acquire higher kinetic energy due to mean free path leading to ionisation of atoms, atoms break into electrons and proton, the electrons in atom can move freely in low pressure. 1. Low pressure gas discharge takes place at 0.4 pa which is very less than atmospheric pressure. 2- the low pressure discharge is used in sodium vapour lamp and fluorescent lamp.

High pressure gas discharge - 1. The high pressure gas discharge take place at a pressure more than 104 pa which is about 20% of atmosphere pressure. 2- the high pressure discharge is utilised in high pressure sodium vapour lamp, high pressure mercury vapour lamp and metal halide lamp.

The process for high and low pressure gas discharge involves that gas atoms or molecules are transferred into excited electronic states by impinging electrons or alternatively by energy transfer from other gas atoms, ions ,molecules. And the excited species emit luminescent light which is either in visible spectrum range or in ultaviolet but sometimes in the infrared.