PURPOSE: To provide a mercury vapor electric discharge lamp, a lighting device therefor and an ultraviolet radiation device using the lamp and the device capable of preventing the blackening of a tube wall for keeping an ultraviolet radiation maintenance factor at a high level, regarding a mercury vapor electric discharge lamp of medium pressure type.

CONSTITUTION: Regarding the mercury vapor electric discharge lamp 1 with mercury sealed over the range of 0.1 to 3.0mm/g per unit capacity in a silica light emitting tube 10 having an electrode 13 sealed for lighting under a tube wall load equal to 10W/cm2 or less, a translucent protection film 14 of metallic oxide is formed on the internal surface of the tube 10. The film formed on the internal surface of the tube 10 acts to prohibit the contact of mercury with silica and prevents mercury ions from being implanted in the defective grill of the silica. As a result, the occurrence of tube wall blackening can be prevented, and a high ultraviolet radiation performance can be maintained over a long term.