High pressure mercury lamp with particular electrode structure and emission device for a high-pressure mercury lamp

Emission device which comprises a high pressure mercury lamp having a fused silica glass discharge vessel containing a pair of opposed electrodes and mercury in an amount at least equal to 0.15 mg/mm3 and rare gas;

• wherein a length L1 (mm) that one of the electrodes projects into the discharge vessel is greater than a length L2 (mm) that the other electrode projects into the discharge vessel;
• and wherein the following conditions are met for a lamp wattage W (watt) and a maximum value of an inside diameter D (mm) of the discharge vessel in a direction perpendicular to an axis which joins the pair of electrodes:
• 0.35×(W)½≦L1≦0.69×(W)½
• L2≦0.76×(W){fraction (1/2.64)}
• and at the same time
• (2.50)e0.0022W≦D≦(5.0)e0.0034W
• and a holding device in which the high pressure mercury lamp is located such that an axis which joins the electrodes is oriented essentially vertically and the electrode which projects into the discharge space with the greater length L1 is located above the electrode which projects into the discharge space with the shorter length L2 into the discharge space.