A gas tube is a sealed glass or metal tube that contains gas at low pressure. It is often used in scientific experiments and applications, such as gas discharge tubes, where an electric current passes through the gas, causing it to emit light. This phenomenon is commonly seen in neon signs and fluorescent lights. Gas tubes can also be used in various types of sensors and devices, including gas detectors and vacuum tubes. They play a crucial role in understanding gas behavior and are essential components in many electronic and lighting technologies.