Investigating the dependence of the temperature of high-intensity discharge (HID) lamp electrodes on the operating frequency by pyrometric measurements

Abstract

Abstract. Phase resolved temperature distributions are determined along a rod shaped tungsten electrode, by which an ac arc is operated within a model lamp filled with argon. Switched dc and sinusoidal currents are applied with amplitudes of several amps and operating frequencies being varied between 10 Hz and 10 kHz. The temperature is deduced from the grey body radiation of the electrode being recorded with a spectroscopic measuring system. Phase resolved values of the electrode tip temperature T tip and of the power input P in are determined comparing the measured temperature distributions with the integral of the one dimensional heat balance with these parameters as integration constants. They are supplemented by phase resolved measurements of the sum of cathode and anode fall called electrode sheath voltage. If a switched dc current is applied it is found that both quantities are within the cathodic phase only marginally higher than for a cathode being operated with a dc current. T tip and P in start to decrease for low currents and to increase for high currents at the beginning of the anodic phase. But with increasing operating frequency the deviations from the cathodic phase are reduced until they cannot be resolved for frequencies of several kHz. A more pronounced modulation but the same tendencies are observed with a sinusoidal current waveform. For 10 kHz a diffuse arc attachment with an almost phase independent electrode tip temperature, which deviates only marginally from that of a dc cathode, and an electrode sheath voltage proportional to the arc current is established with both current waveforms.

Investigating the gas phase emitter effect of caesium and cerium in ceramic metal halide lamps in dependence on the operating frequency

“…Reliable results were obtained with this method for electrodes operated with a dc-current [1,6,11]. But if the electrodes are operated with an ac-current the modulation of the electrode temperature is limited to a small area behind the electrode tip [15]. Therefore also the tip region with its exaggerated values of has to be taken into account when the integral of the heat balance is matched to the measured temperature distribution.…”

“…In this case it is easier to identify and remove locally excessive temperatures. A detailed discussion of the limited measuring accuracy of T tip is presented in [15,26]. It was shown that the phase resolved experimental determination of T tip is afflicted with an error of the order of ∆T tip ≈ 50 K.…”

“…By an inverse Abel transformation of I L (y) radial emission coefficients L (r) are obtained if the discharge is rotational symmetric. Table 4: Spectroscopic data for the calculation of the plasma temperature T pl from Hg-line intensities [38] At first the plasma temperature T pl inside a YAG lamp is determined using two overlapping mercury lines at λ 1 = 576.96 nm and λ 2 = 579.07 nm [15,24,37]. The corresponding spectroscopic data is given in table 4 with the transition probabilities A 1 and A 2 , the statistical weights g 1 and g 2 and the excitation energies of the upper line levels E 1 and E 2 .…”

“…If pure tungsten electrodes are used the temperature of the electrode tip is raised up to its melting point, T m = 3695 K, to supply a sufficiently high thermionic electron emission for a diffuse attachment of the lamp arc on the electrodes [9,10,11,12,13,14,15]. But the work function and with it the electrode temperature can be substantially reduced if a dipole layer consisting of a monolayer of atoms being electropositive with respect to tungsten is deposited on the tungsten surface.…”

Investigating the influence of the operating frequency on the gas phase emitter effect of dysprosium in ceramic metal halide lamps

“…The behaviour of tungsten electrodes for HID lamps was investigated recently in the so called Bochum model lamp filled with argon [6] in dependence on the operating frequency being varied between 10 Hz and 10 kHz [28]. The Bochum model lamp is formed by a quartz tube, sealed vacuum-tight by two metallic end pieces with feedthroughs containing movable holders for the tungsten electrodes.…”