Abstract: A high-pressure sodium discharge lamp has a coil electrode wound on a stem which extends axially into a metal tube whose end is sealed into the wall of the lamp envelope. Outside the envelope the tube is rolled or crimped on to the stem and sealed to the stem by brazing.

Abstract: An electric lamp assembly for use in sealed beam lighting units comprises a sealed envelope containing a light source mounted in an integnally flanged cap. Electrical supply leads pass through hermetic seals in the cap, and means are provided which support the light source in a predetermined position relative to the cap flange.

Abstract: A high-pressure mercury/metal-halide discharge lamp has the discharge electrodes offset below the central axis of the arc tube to increase the uniformity of the wall temperature and improve the performance of the lamp. The upper part of the arc tube wall is shaped to be nearer the electrodes at the ends and further from them at the center than in a cylindrical tube.

Abstract: An electric discharge lamp includes a structure within the discharge envelope comprising a source of at least one halogen, metal or metal halide to serve as an arc-modifying additive, enclosed in the structure from which it is capable of being released into the discharge envelope upon subsequent treatment, for example on heating or on striking an arc. The structure preferably comprises a hollow carrier body of refractory metal, in which the source of halogen, metal or metal halide is disposed, and may be covered by a closure of porous sintered refractory metal or of fusible metal. The fusible metal may be inert as regards the discharge and may itself affect the emitted radiation characteristics. The structure may constitute one electrode of the lamp, and may also include electron-emissive material. It has the advantage of protecting the additives from the atmosphere and thereby simplifying manufacture of the lamp.

Abstract: A ballast circuit for a discharge lamp uses simply a capacitor in series with a relatively small inductor the capacitative reactance being between 24 and 55 times the inductive reactance. At these values the third harmonic distortion is unexpectedly low, while the crest factor (ratio of peak to r.m.s. current) is still within acceptance values. Because the inductor is small the efficiency of the circuit is high, and its cost and weight reduced. The capacitance/inductance ratio can be equated to the ratio of the frequency of the tuned circuit to the supply frequency, and on this basis the preferred range is defined by 5 to 71/2 times supply frequency.

Abstract: A cold-light mirror, especially suitable in the form of an ellipsoidal or hyberbolic mirror for an optical system for forming a light beam, comprises a metal substrate covered with a pigmented vitreous layer for absorption of infra-red radiation which is transmitted by an overlying dielectric interference layer.

Abstract: A lighting unit has a lamp supported in position relative to a reflector by means of a support including a holder which clasps an end seal of the lamp envelope or capping box fitted to the end seal, a co-operating rib and groove in the holder and end seal or in the holder and the capping box serving to locate the lamp against axial movement. For a double-ended lamp two holders are provided on a common support.