Effect of Electron Deexcitation and Self-Absorption on the Intensity of the Hg 2537-Å Radiation from Hg + Ar Discharges (ac Fluorescent Lamps)

The intensity of the Hg 2573-A radiation from Hg + Ar discharges was measured as an independent function of mercury pressure (0.2-50 mTorr), ac current (50-2100 mA) and tube radius (0.79 cm and 1.27 cm) at a constant Ar pressure of ~4 Torr. For various constant mercury pressures, the Hg 2537-A intensity initially rises linearly with increasing current, but then tends to bend over and approach an asymptotic limit. The nonlinear, asymptotic behavior is due to electron deexcitation of the Hg 6(3)P(1) state at the higher currents in the presence of Hg 2537-A self-absorption. The Hg 2537-A intensity was also measured as a function of mercury pressure at various constant currents. The intensity rises to a peak (which defines an optimum Hg pressure) and then decreases with further increase in mercury pressure due to the combination of self-absorption and electron deexcitation. For high ac currents, the optimum Hg pressure is independent of current but varies inversely with the tube diameter. All this behavior is relevant to the problem of obtaining high efficiency from fluorescent lamps at high powers.