Mercury lamp of the short arc type

摘要

A mercury lamp of the short arc type with a high degree of maintenance of irradiance is achieved in a mercury lamp of the short arc type by the cathode containing thorium oxide and having a tungsten carbide layer on its surface except at tip end area, by at least one of the cathode or anode being provided with metallic tantalum, and by the condition 1.56 ≤ VT/SC being satisfied, where SC is the area of the tungsten carbide layer (cm<2>) and VT is the volume of the metallic tantalum (mm<3>). Alternatively, a high degree of maintenance of irradiance can be achieved in a mercury lamp of the short arc type by the condition 0.043 ≤ VT/VW being satisfied, where VW is the volume of the anode (cm<3>) and VT is the volume of the tantalum in the lamp bulb (mm<3>). <IMAGE>