Abstract: In a short-arc high-pressure discharge lamp (1) with a xenon fill for digital projection purposes, the separation L in mm of the two mutually facing end sections (6a, 8c) of the cathode (6) and the anode (8) when the lamp is hot is given by the relationship 0.8×P≦L≦1×P+1, where P is the lamp power in kW. Further, the diameter D of the circular-cylindrical middle section (8a) of the anode (8) in mm obeys the relationship D≧2.1×L+10.

Abstract: In a short-arc high-pressure discharge lamp (1) with a xenon fill for digital projection purposes, the separation L in mm of the two mutually facing end sections (6a, 8c) of the cathode (6) and the anode (8) when the lamp is hot is given by the relationship 0.8×P≦L≦1×P+1, where P is the lamp power in kW. Further, the diameter D of the circular-cylindrical middle section (8a) of the anode (8) in mm obeys the relationship D≧2.1×L+10.

Abstract: A metal-halide discharge lamp for photooptical purposes has a small electe spacing of less than 15 mm, preferably 2-8 mm, to provide an essentially pin-point light source, and a fill which contains AlI.sub.3 in an amount between 0.1 and 4.5 mg/cm.sup.3. Other filling components may in particular be halides of mercury, indium, thallium or cesium; up to 2 mg/cm.sup.3 of AlBr may be added. The lamp is particularly adapted for combination with a, preferably parabolic, reflector.

Abstract: A metal halide gas discharge lamp for projection purposes includes a discge vessel closed at both ends preferably has between the electrodes a central frosted partial area applied on the outer surface of the discharge vessel. The relationship 0.1<B.ltoreq.1, preferably 0.4<B/d<0.8, applies to the quotients of the width B of the frosted partial area by the inter-electrode gap d. The lamp is optionally provided on one or both sides with heat build-up coatings. The lamp advantageously forms a unit with an optical reflector.

Abstract: To improve the arc stability of high-pressure discharge lamps, particularly f power ratings of up to about only 250 W, the cathode (4) is formed as an elongated, essentially cylindrical base body (8) having a tapering, conical region (9) terminating in a tip (10). The base body (8), only, is covered with a carbide coating along its length, except for an end portion for electrical connection; the carbide coating starts at the junction or transition between the cylindrical base body portion and the conical end portion. This cathode construction is easier and cheaper to make than prior art cathodes, by coating an essentially cylindrical cathode and then etching or grinding and polishing the tapering end region (9). The electrode is preferably made essentially of tungsten, doped with thorium oxide present up to about 0.6%, optionally also potassium, aluminum and silicon in tiny amounts. The electrode spacing is between 0.4 to 0.

Abstract: To prevent corrosion of molybdenum connecting pins or wires extending from elt-sealed ends of high-power lamps, the region immediately adjacent the exit points from the melt-sealed end are cooled by a cooling gas, for example air or an inert gas such as nitrogen. The cooling gas is applied by cooling ducts which are made of metal and, simultaneously, provide for electrical connection of electrical energy to the connecting leads. Cooling gas can be introduced either through terminal pins or rods into the tubular elements, or the tubular elements can be connected, as usual, to the part-solid terminal pins or rods and additional gas connections are passed through the base through the tubular elements to supply cooling gas.