Dear student,
Emission spectra:
When an element is heated strongly, or when a gas at low pressure is  subjected to a high electric potential, the element begins to glow,  indicating that it is emitting energy in the visible region of the  spectrum. This arises from electrons that have absorbed a certain amount  of energy and have been promoted to a higher energy state. When the  electrons revert to a lower energy state, they lose energy by emitting  photons whose energy corresponds to the energy loss, E. From Planck's law, E = hc/λ,
Absorption spectra:
The spectrum of white light shows an uninterrupted change in colour from  red to violet, as shown above. In 1814, Fraunhofer, while repeating  Newton's famous dispersion experiment using his own invention, the  spectroscope, found that the spectrum of light from the sun showed a  great many dark lines, which came to be known as "Fraunhofer lines".
 









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