High pressure electric discharge lamp

In a high pressure electric discharge lamp including a discharge envelope which contains a filling consisting of mercury, rare gas, and at least two metal halides which are vaporizable at the operating temperature of the lamp, and which has mounted within it a pair of tungsten electrodes between which an electric discharge passes through the filling in operation of the lamp, each said electrode being attached to an electrically conducting lead extending to the exterior of the discharge envelope and connected to a terminal carried by an outer envelope of light-transmissive vitreous material in which the discharge envelope is enclosed, the improvement consisting of, in combination,

• the incorporation within a cavity in the structure of each said electrode of a quantity of activator material consisting essentially of scandium oxide, the said activator material being in the form of a solidified melt substantially filling the said cavity and adherent to the electrode structure, and
• the provision in the discharge envelope of said filling in which the metal halides consist of at least one metal iodide and at least one metal bromide, including at least one member of the group consisting of scandium iodide and scandium bromide, in relative proportions such that the percentage atomic ratio of the total amount of bromine to the total amount of iodine in said metal halides is in the range of 20:80 to 60:40.