Physics of mercury-free high-pressure discharge lamps

Abstract

This paper gives a summary of recent results about the replacement of mercury in high-pressure discharge lamps by metallic zinc. Actually, this topic is of high relevance for the lighting industry due to the need for more environmentally friendly products. Due to upcoming European legislations which are expected for the year 2003, the replacement of mercury in lighting products is a high priority task. For example, mercury-free headlight discharge lamps are requested by the automotive industry.Pure zinc/argon discharges as well as lamps including zinc or mercury and metal halide additives are investigated. Experimental data are compared with model calculations of the energy balance involving the transport of heat and radiation. Since the excitation energies of relevant zinc transitions are lower than for mercury, axis temperatures of pure zinc lamps are about 300 K below the value of mercury arcs. In addition, the thermal conductivity of zinc including the contribution of radiation diffusion is larger than compared to mercury. From lamp voltage measurements it is found that the cross section for elastic electron scattering by zinc atoms is about the same as for mercury. When adding metal halides to a pure zinc discharge with argon as a starting gas, i.e. NaI, TlI, DyI 3 , axis temperatures decrease to about 5100 K due to strong radiation cooling. In order to obtain sufficiently large lamp voltages, wall temperatures of more than 1300 K are adjusted by means of polycrystalline aluminaoxide (Al 2 O 3 ) as a wall material. Electric field strengths of 6.0 and 8.6 V mm −1 are measured for metal halide lamps containing zinc or mercury, respectively. The light technical data of the discharges are very close, since mercury and zinc do not contribute significantly to the radiation in the visible range. Efficacies of up to 93 and 100 lm W −1 are found in metal halide lamps with zinc and mercury, respectively. Consequently, zinc turns out to be an attractive replacement for mercury in this type of lamp not only from an environmental point of view.

Experimental and theoretical cross sections for elastic electron scattering from zinc

“…As a consequence, testing this representation on a heavier atom, where relativistic effects might be important, is a valid rationale for its study. The second reason is applied, and largely stems from the work of Born [4,5], who suggested that Zn might be an attractive replacement for mercury in making high-pressure gas discharge lamps more environmentally friendly. More recently, studies on the emission dynamics of an expanding ultrafast laser-produced Zn plasma have been reported [6,7].…”

“…That collisional radiative model included the RDW elastic integral cross section (ICS), as well as the ICSs for discrete inelastic processes, to ensure that the sum of their individual ICSs was consistent with the total cross section and therefore that their [7] cross-section data base was self-consistent. As a consequence of the Born [4,5] work, White et al [8] conducted an initial multiterm simulation study looking at the transport characteristics of a swarm of electrons drifting through a background Zn vapor under the influence of an external electric field. That work of White et al [8] demonstrated that anisotropic scattering, through incorporation of the elastic momentum transfer cross section [8] of Zn, was necessary for accurately describing the electron transport characteristics in Zn under the influence of such an applied (external) electric field.…”

Simulation of the A–X and B–X transition emission spectra of the InBr molecule for diagnostics in low-pressure plasmas

“…Several properties of mercury are hereby utilized such as a high vapour pressure and the strong and efficient radiation in the visible and especially the ultraviolet spectral range. Recent research both in low and high pressure lamps ( [1,2,3] and [4,5]) focuses on finding efficient substitutes for mercury due to its toxicity. Molecular radiation -especially from metal halides -is under discussion to be a good alternative to mercury [6].…”

Mercury-free high pressure discharge lamps dominated by molecular radiation

“…The straightforward strategy for mercury replacement is a direct substitution of mercury by a substance with similar high vapor pressure, corresponding momentum transfer cross-section as well as similar radiation properties [4][5][6][7].…”