Line Broadening

Line broadening refers to the phenomena where spectral emission lines are seen at wavelengths other than the predicted wavelengths of transitions of the electrons in the atom. This can be caused by a number of factors, namely
 * natural
 * Doppler
 * collisional

Natural Line Broadening
Natural line broadening is always present, but can only be observed when Doppler and collisional broadening is not present

Doppler Line Broadening
Doppler line broadening is caused when the gas particles in question is moving relative to the light source. This is caused mainly by random motions linked to the temperature of the gas. As such, it can be observed in gas with high temperature but low pressure. Broadening happens because when they are moving apart relatively, the gas sees a redshifted light, which means that a shorter wavelength light can also be absorbed by the gas. The opposite is true when the gas particle and the light source are moving towards each other relatively. A longer wavelength light is blueshifted and has the possibility to be absorbed.

Collisional Line Broadening
Collisional line broadening occurs when gas particles bump into one another and distort their energy levels. This can be seen in gasses of high pressure and high temperature