FIG. 8-8 (a) Part of the emission spectrum of sodium. Each bright line represents a specific frequency in the light given off when sodium vapor is excited in an arrangement such as that shown in Fig. 8-7. Every element emits a set of frequencies that is characteristic of that element. (b) Part of the absorption spectrum of sodium. Each dark line represents a specific frequency in the light absorbed by sodium vapor when white passes through the vapor. Every dark absorption line corresponds to one of the bright lines in the emission spectrum of the same element.