Potentialities of neon xenon pulsed discharges for publicity and architectural lighting

Abstract

Summary form only given. As mercury is a non environmental friendly element, many efforts are made in the field of light sources in order to replace Mercury-based lamps. This contribution deals with the potentialities of Neon Xenon discharges for replacing Mercury ones used in cold hollow cathodes fluorescent tubes. Interest of pulsed excitation (pulse duration: few mus; pulse frequency: few kHz) had been already shown in our previous works in comparison of AC mode. Following parametric studies on pressure (on the range 10 mbar-100 mbar) have shown that a pulsed Ne-Xe discharge at advanced pressure is able to provide close to 50% of illuminance provided by a mercury tube supplied with a 25 mA sinusoidal excitation current. Working times of thousands hours have been reached without significant decreasing of the luminous flux. Spectroscopic analysis and simple computed simulations have improved comprehension of mechanisms leading to the phosphor excitation, and permits to clarify results of parametric studies: in particular, neon partial pressure has been clearly identified as a fundamental parameter which determines the density of ionic excimers (essentially Xe2 +) whose recombination efficiently populates Xe first resonant level during post-discharge period. Its de- excitation to the ground level produces a significant VUV emission (147 nm) able to excite phosphor. As post- discharge emission typically occurs on few hundreds of mus, duty cycle must be adapted to fully recover VUV emission. Ignition processes have also been investigated. Strong influence of the excitation frequency on breakdown has been observed: residual electronic density from previous pulse increases with the frequency. Consequently, ignition in hollow cathode is accelerated and breakdown voltage decreases. Compromise has to be found between pulse frequency and duty cycle in order to have the breakdown voltage as low as possible while fully recovering post- discharge emission.