Spectrum Tubes These tubes are ideal for acquainting students with the spectra of better known gases in their pure form and for wavelength determination. The glass tubes are 25 cm long with the capillary portion about 10 cm long. An electrode is sealed in each end and attached to a metal end cap with a loop for convenient hookup to wire connections. Spectrum tube assemblies can be used in a variety of spectroscopic applications. When observed through a spectroscope the emission lines corresponding to the energy transition levels of the gaseous atoms or molecules will appear as distinct components. These research grade tubes are specially designed to provide optimum intensity and line resolution. Recommended for use with our Spectrum Tube Power Supply.