REVIEW OF METAL-HALIDE DISCHARGE-LAMP DEVELOPMENT 1980-1992

Of all high-intensity discharge (HID) lamps, the metal-halide lamp has attracted considerable attention and raised market expectations through its diversified product range covering a wide range of lighting applications. This has led to increasingly complex solutions to achieve the desired characteristics. Extensive studies on lamp design, iodide reactions with the fused-silica-tube wall and the electrodes, effects of impurities, loss of sodium etc. have been already carried out. Recently, rare-earth metal (Dy and Tm) metal-halide lamps have attracted increasing interest owing to their excellent colour rendering properties. As a result, research concentrating on reactions with the fused-silica-tube wall and the electrodes has also been increasing. It has become clear that rare-earth metal-halide lamps such as Dy and Tm types have major chemical and technical differences compared with the Sc-Na lamp, particularly in the reaction between iodide and the fused-silica-tube wall with an effect on the transport phenomenon of silicon and silica. This phenomenon has resulted in a need for different measures to counteract tube-wall blackening and electrode corrosion. Other topics examined include the practical use of lamps with built-in ignitors, compact lamps with good colour rendering, and applications of miniature metal-halide lamps for general lighting, in car headlamps, for projection television.