Fluorescent lights contain spectral lines from the light emission of mercury atoms. Special coatings on the inner surface of the bulb help to accentuate visible frequencies, which can be seen through the diffraction grating reflection of a compact disc (CD). Cut a narrow slit through some thick paper (or thin cardboard), and place it over a bright fluorescent bulb. View this slit at an oblique angle against a CD and look for spectral lines. Place the slit over an incandescent bulb, and you’ll see a smooth, continuous spectrum (no lines), because the incandescent filament glows at all visible frequencies. Try looking at different brands of fluorescent bulbs. You’ll also be able to see spectral lines in street lights and fireworks. For those it is best to use “rainbow” glasses, which are available from a nature, toy, or hobby store.