Continuum emission spectra from long linear xenon discharge lamps with metallic halide additives.
The behavior of long linear xenon discharges with metallic halide additives in narrow-bore quartz tubes is described. For various lamp applications, these discharges may have several desirable characteristics: (1) controllable line emission or continuum emission as desired, with excellent color rendition, (2) reasonable efficiency, (3) fast startup (~20 sec), (4) elimination of the need for mercury and its pollution hazard, (5) possible efficient operation in the range between a few watts per linear cm and ~30 W/linear cm. The present lamps are in the laboratory stage, and several problems remain to be solved. It is argued that the continuum emission which sometimes appears in these xenon + metallic halide discharges (and also in commercial mercury arc lamps with certain metallic halide additives) is correlated with a high vapor pressure of the metallic halide additive. Thus, this continuum may be due to either molecular radiation or transitions involving free electrons originating copiously from the ionization of the metallic additive which has a comparatively low ionization potential. If a sufficiently high vapor pressure of any metallic halide can be achieved in the discharge, then a continuum emission seems to be a fairly common phenomenon. A scheme for achieving this objective is described.
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