We have examined the properties of mercury–rare-gas discharges operated at low fields where volume ionization is negligible. The discharge current is due to thermionically produced electrons and is limited by the electron mobility. The mixtures consisted of mercury and either Ar, Kr, or Xe at 30–760 Torr. Temperatures were varied from 50 to 250 °C. uv and visible radiation production, as well as electrical properties, were measured and compared to theoretical calculations. The measured positive volt-ampere characteristics agree well with theory. The calculated efficiency for excitation of Hg3P1in these discharges is greater than 50% over a wide range of conditions. The low measured radiation production efficiency (less than 5%) is consistent with model calculations which include quenching of the3P1by Hg and the rare gas to the3P0state and its subsequent decay by the formation of mercury excimers.