What's is the difference between the absorption spectrum and the Emission spectrum?

If you shine sodium light thru a cold gas, the lines of the sodium spectrum will be suppressed if you look for these lines coming from the gas because of excitation of the gas molecules.

If the light from a sodium vapor lamp is examined (perhaps by a spectroscope) the lines from the sodium spectrum will appear quite bright because of the excitation of the gas within the sodium lamp.

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