2008 Volume 92 Issue 11 Pages 775-782
Discharge lamps that have electrodes are classified into two categories, hot cathode lamps (HCLs) and cold cathode lamps (CCLs). We investigated the relationship between the presence of Hg, the kinds of rare gases present, and the cathode fall voltage (CFV) of both CCLs and HCLs. The results show mainly two points. One is the difference in the CFV characteristics, that is, CCLs’ CFV is positive, while HCLs’ is negative. This is because the emission mechanism of CCLs, due to the gamma effect, differs from that of HCLs due to the Schottky effect. The other main point is the influence of Hg on the CFV. The CFV of CCLs increases when Hg is present because of the difference between γ-coefficients for Ne+ and Hg2+ due to the energy potentials. The CFV of HCL also increases when Hg is present because of the difference between the cathode temperatures in an Ar discharge and an Ar-Hg discharge.