Abstract: A method of and apparatus for setting the orientation of a single crystal which may be a seed crystal, boule, wafer or a growing boule. The crystal is irradiated with a beam of X-rays having a peak of energy at a given wavelength and the orientation of the crystal is adjusted while moving the crystal and the beam about an axis perpendicular to the equatorial plane containing the X-ray beam until a pair of reflexions that are symmetrical with respect to the equatorial plane occur simultaneously at the said wavelength of radiation. When the X-ray beam has a peak of energy at the said wavelength against a back ground of white radiation, symmetrical reflexions can be detected and will flash simultaneously only when one of the crystallographic planes of symmetry is set in a predetermined or determinable orientation relative to a given datum.

Abstract: Metal halide discharge lamps based on sodium and scandium iodides show improved color rendering without important loss of efficacy by the inclusion of lithium iodide, especially in the molar proportion of 10-50% LiI based on the total of Li, Na and Sc iodides. The ratio of alkali metal of SC iodides should be between 5.4:1 and 57.5:1. Especially preferred are lamps with less than 10 molar % ScI and the lamps may additionally contain caesium iodide to broaden the emission spectrum.