Spectrum Tubes
Spectrum tubes are glass tubes filled with a gas, usually that of an element or small molecule. Sealed metal electrodes are located at the ends of each tube. When a spectrum tube is placed in a spectrum tube power supply and the power supply is turned on, an electrical discharge is passed through the tube, causing electrons in the gas to be excited. As the electrons relax, they emit light-a characteristic color for each gas.
This is the basis on neon lights.
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