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 throu gh its diversified product range covering a wide range of lighting app lications. This has led to increasingly complex solutions to achieve t he desired characteristics. Extensive studies on lamp design, iodide r eactions with the fused-silica-tube wall and the electrodes, effects o f impurities, loss of sodium etc. have been already carried out. Recen tly, rare-earth metal (Dy and Tm) metal-halide lamps have attracted in creasing interest owing to their excellent colour rendering properties . As a result, research concentrating on reactions with the fused-sili ca-tube wall and the electrodes has also been increasing. It has becom e clear that rare-earth metal-halide lamps such as Dy and Tm types hav e major chemical and technical differences compared with the Sc-Na lam p, particularly in the reaction between iodide and the fused-silica-tu be wall with an effect on the transport phenomenon of silicon and sili ca. This phenomenon has resulted in a need for different measures to c ounteract tube-wall blackening and electrode corrosion. Other topics e xamined include the practical use of lamps with built-in ignitors, com pact lamps with good colour rendering, and applications of miniature m etal-halide lamps for general lighting, in car headlamps, for projecti on television.