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The electron density at the axis, the electron temperature and the electric field strength of the positive column of low-pressure Hg/Ne discharges have been measured using electrostatic probes. The measurements have been carried out for discharge currents between 0·1 and 0·8 A, noble gas pressures between 0·3 and 10 Torr, tube wall temperatures in the range of 13-70°C, and an inner tube radius of 18 mm. The addition of argon to neon as a filling gas has also been studied.By computing the volume and wall losses from the measured data, the authors have worked out the effect of the discharge conditions on the radiation efficiency of the column. These data have been compared with the results of a theoretical model of the positive column, showing a reasonable agreement. From this comparison it has been found that elastic collisions of electrons and of ions with neutral mercury atoms have a decisive influence on column properties at mercury pressures above similar 10−2 Torr. Furthermore a higher radiation efficiency of the column has been found in Hg/Ne discharges compared to Hg/Ar discharges for 3 Torr noble gas pressure, wall temperature 42°C, and discharge current 0·4 A.

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