Principles of Light Generation


How can Light be generated

There are basically just two practicable ways of generating light:

  • Incandescence  
  • Luminescence in solid and gaseous media


The way in which electric light in particular is generated determines to a great extent the inherent characteristics influencing the visual process. Also the efficiency with which electrical energy is converted into visible radiation varies widely from one light source to another.this also has a bearing on the spectral composition of the light generated,which is why the relation between quantity,quality and cost effectiveness of artificial light  is so complex.

Classification of Light Sources

There is no basic difference between natural and artificial light.

Incandescence


The oldest and still the most widespread way of generating light is by bringing a solid body to incandescence by heating.The high temperature necessary to bring a body to incandescence material itself or by employing some type of solid,liquid or gaseous fuel. Another method is to pass an electric current through a circuit incorporating a component of a relatively high electrical resistance.
An example is an  electric lamp using  incandescent filament .

Luminescence


Luminescence produces either a line or a  band spectrum. It is the light effect produced by the excitation of single valence electrons of an atom,with little or no interference from neighboring
atoms.Luminescence manifested in the form of gaseous discharge often supported by fluorescence,that is widely used for practical illumination purposes.

Gaseous Discharge


It is generally obtained by sending an electric current through a gas between two solid conductors named electrodes.
for the purpose of light generation it is important to differentiate according to gas pressure between low and high pressure discharges and according to the electrode temperature between glow and arc discharges.

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