Patent ID: 7800309

Claim:
A mercury vapor discharge lamp comprising: a lamp envelope enclosing, in a gastight manner, a discharge space provided with a filling of mercury and a rare gas, the lamp envelope comprising discharge means for maintaining a discharge in the discharge space, the lamp envelope allowing UV-light to pass, the lamp envelope being made of a black glass component, the composition of the black glass component being free of PbO and comprising, expressed as a percentage by weight, the following constituents: SiO 2 55-70 MgO 0.01-3 CaO 5.1-6 CoO 0.2-0.4 NiO 1.7-3.25 Fe 2 O 3 0.01-1 the black glass component further comprising Li 2 O, Na 2 O, and K 2 O, the sum of the concentrations of Li 2 O, Na 2 O, and K 2 O being in the range from 13 to 18% by weight, the black glass component further comprising SrO and BaO, the sum of the concentrations of SrO and BaO being in the range from 8 to 13% by weight.