An ultrahigh pressure mercury lamp which is small and has high light radiation
intensity and moreover good color reproduction with high efficiency in which, even
with a large amount of mercury added, a failure of the mercury to vaporize in the
bulb part does not occur, and in which blackening of the bulb part due to wearing
of the electrodes even under a large electrode load as a result of shortening of
the distance between the electrodes is low is obtained by an ultrahigh pressure
mercury lamp in which a bulb part of the discharge vessel made of translucent material
has an essentially ovoid shape, is filled with at least 0.2 mg/mm3 of
mercury and which is operated at an input wattage of at most 400 W using direct
current, has the length D of the tip area of the anode and the length L of the
bulb part in the direction of the tube axis of the lamp set in accordance with
the relationship DL/2.
