Axial segregation in metal–halide lamps under varying gravity conditions during parabolic flights

Abstract

Metal-halide lamps have high efficiencies. These lamps often contain rare-earth additives (in our case dysprosium iodide) which radiate very efficiently in the visible spectrum. Colour separation is a problem in these lamps; this is caused by axial segregation of these additives as a result of diffusion and convection. To vary the effect of convection, parabolic flights were performed with micro-gravity (0g) and hyper-gravity (∼1.8g) phases. During these flights, the atomic dysprosium density was measured by means of laser absorption spectroscopy. In addition, the lamp voltage, which is strongly influenced by the total amount of Dy in the lamp, was measured. The Dy density and axial segregation are dependent on the gravity. The dynamic lamp behaviour during the parabolas was investigated: the dysprosium density and lamp voltage followed the gravity variations. When entering the micro-gravity phase, the axial diffusion time constant is the slowest time constant; it is proportional to the mercury pressure in the lamp.

Imaging laser absorption spectroscopy of the metal-halide lamp under hyper-gravity conditions ranging from 1 to 10g

“…The specifications of the lamps are given in table 1. For the calculation of the pressure an effective temperature of T eff = 3000 K is assumed [17,29]. Due to deterioration of the lamp, some deviations from the predicted values can be observed.…”

Metal-halide lamps in micro-gravity: experiment and model

“…The experiments verify the model results, whereas the model aids the interpretation of the experimental results. The experiments are part of a poly-diagnostic study [5][6][7][8][9][10][11] of the metal-halide lamp.…”

Time Evolution of Optical Emission Spectrum of a Hg-HID Lamp Exposed to X-ray

“…In some mercury HID lamps, if the pressure is sufficiently high the 253.73 nm line is missing in the stable regime because most probably it is reabsorbed in the outer region of the plasma [7]. This is supposed to be caused by the high density of metal atoms in highpressure discharge lamps [9], which is even higher in the colder plasma regions.…”

“…Many theoretical models [1][2][3][4][5] have been created and a lot of experimental work [6][7][8][9] on plasma of high-intensity discharge (HID) lamps have been carried out. It is known that different internal and external parameters can influence the emission spectrum of a high intensity discharge (HID) lamp: plasma composition, electrode material and shape, the lamp current, the envelope, internal pressure, external temperature and other factors.…”