Keep the incandescent bulb lit, and at the same time provide a flourescent light source. Have the student view one and then the other. Describe the differences they see. When gases glow they emit light - but not all colors of light. So a few colors are missing in it's spectrum.
Incandescent bulbs produce a 'Continuous spectrum'.
Flourscent lights produce a spectrum with certain wavelengths missing. Viewing the spectra of other gases. If available, discharge other gas specturm tubes. Have students view these one at a time, first with their eyes and tell what colors they see, then with the spectrometers and tell what color lines they see. Spend some time having students record the spectral lines they observe on paper.