Metal halide discharge lamp with a quartz discharge vessel and an outer UV radiation absorbent envelope

A metal halide lamp having a discharge vessel (2, 22) made of quartz glass;

• a light transmissive outer envelope (3, 23) surrounding the discharge vessel (2, 22);
• electrodes (4, 5;
• 24, 25) in said discharge vessel;
• current supply wires (8, 9;
• 28, 29) electrically connected to said electrodes and extending from said discharge vessel within and into said outer envelope (3, 23);
• and
• an ionizable fill which includes sodium or a sodium compound gas-tightly retained in the discharge vessel (2, 22),
• wherein the sodium content in the ionizable fill is at most 0.7 mg/cm.sup.3 of the discharge volume;
• and comprising means to reduce loss of sodium from said ionizable fill due to sodium migration resulting from photo-ionization at the current supply wires upon impingement of UV radiation on the current supply wires,
• said means comprising a doping material added to said outer envelope (2, 23), which doping material has the characteristics of rendering the quartz glass of said outer envelope UV radiation absorbent, whereby the UV radiation impinging on said current supply wires is attenuated;
• said means further including
• a distance or space of the outer envelope (3, 23) from the discharge vessel (2, 22) of at most 5 mm, and
• the space between the outer envelope (3, 23) and said discharge vessel (2, 22) being evacuated.