Xenon is used as a " starter gas " in high pressure sodium lamps . It have the lowest thermal conductivity and lowest ionization potential of all the non @-@ radioactive noble gases . As a noble gas , it do not interfere with the chemical reactions occurring in the operating lamp . The low thermal conductivity minimize thermal losses in the lamp while in the operating state , and the low ionization potential cause the breakdown voltage of the gas to be relatively low in the cold state , which allow the lamp to be more easily started .