Abstract: In an arc tube for a high intensity metal halide discharge lamp, a particular composition of metal halide dose is provided to control thorium transport to the electrodes within the arc tube and tungsten transport to the wall to improve arc tube performance.

Abstract: High pressure discharge lamps containing a fill of mercury and metal halides, having a power input of 250 watts or below and useable for general illuminating purposes achieve higher efficacy by developing high end temperatures without excessively obstructing the transmission of light and without creating excessive thermal losses through radiation and conduction. To reduce the obstruction of light, heat-conserving coatings on the lamp ends are preferably omitted and small neck seals are used which serve also to reduce thermal losses. The lamps are constructed with an aspect ratio of arc chamber length to diameter from 0.9 to 2.5 and with an electrode insertion factor from 0.1 to 0.6 and operate with a wall loading from 10 to 35 watts/cm.sup.2 and with an arc loading from 60 to 150 watts/cm.

Abstract: A metal vapor arc lamp having a filling including pyrolitically decomposing metal halides such as thorium iodide uses a loop electrode which allows the heat from the hot spot to flow in two directions. Such electrodes are less expensive to manufacture and, in an environment where the decomposing metal halide provides activation, they are less subject to deformation and consume less energy than conventional electrodes comprising shank plus overwind.