The black areas are were wavelengths are not emitted by neon. No light is emitted with those wavelength values. The many lines are the colors of visible light emitted by excited neon atoms.

neon emission spectrum showing the many orange to red emission lines for neon

 

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continuous spectrum for reference scale

The spectrum has markers to help locate the 400nm , 500 nm, 600 nm , 700 nm, wavelength positions. This spectrum is supposed to be used to estimate the locations of the lines in the neon spectrum.