High luminance metal halide lamp containing ScBr/sub 3/ for LCD projectors

Summary form only given, as follows. Recently the needs of high luminance and good color rendering light sources for LCD projectors have increased. Metal halide lamps are widely used for LCD projectors because of their good color rendering and high efficacy. Their luminance, however, are so low that it is difficult to achieve a bright screen with projectors in which the metal halide lamps are used. This study reports excellent characteristics of the new 250 W metal halide lamp with 2.0 mm arc length which have higher luminance. Our new metal halide lamp contains ScBr/sub 3/. The ScBr/sub 3/ lamp achieves more than 2 times as high luminance as the prior metal halide lamp which contains InI and HoI/sub 3/. This result is due to the high ionization potential of Sc and high vapor pressure of ScBr/sub 3/. Ionization potential of Sc (6.7 eV) is higher than that of In (5.8 eV). Also the vapor pressure of ScBr/sub 3/ (7000 pa at 1100 K) is higher than that of HoI/sub 3/ (80 pa at 1100 K). Higher ionization potential makes an arc thinner. Higher vapor pressure increases the amount of radiation. Therefore higher luminance is achieved. Luminance of the ScBr/sub 3/ lamp is approximately the same as that of ultra high pressure mercury lamps. In addition the ScBr/sub 3/ lamp has strong line emission around the 630 nm wavelength. So the color rendering of the ScBr/sub 3/ lamp is better than that of ultra high pressure mercury lamps. We confirm that by use of ScBr/sub 3/ metal halide lamps are closer to the ideal light source for LCD projectors, especially small scale portable TV projection systems.