The white light emitted from a neon discharge tube at its initial discharge, changes to red gradually with the time of discharge. This aging phenomenon was studied by a spectroscopic method. The white light mainly was that of Ångström bands of CO molecules. The recombination of carbon atoms and oxygen atoms produced by the dissociation of CO molecules in the tube was arrested by the neon gas. The carbon thus freed, therefore, was fixed on the wall of the tube gradually. This was the main cause giving the phenomenon. The similar phenomenon was also observed in the case of helium discharge tubes.