The gas neon is a colorless gas, which is not interesting at all to display. One could equally well display a bottle full of air. The inert gas neon, however, is very interesting, when used in a gas discharge tube at low pressure. When a high voltage is applied to a tube, filled with neon at low pressure, then a current flows and a very bright orange/red light is produced. Of all inert gases, neon produces the brightest light for a given power input to the discharge tube. For this reason, neon is used very much in all kinds of signs, ranging from commercial shop and restaurant signs to signs, used for directing traffic. The picture shows a tube of approximately 20 cm length, which is connected to a 3300 V AC source, in series with a 5 MΩ resistor in order to limit the current.