Gasentladungslampe

A protective layer of BaSO4 or BaSO4 mixed with SiO2 is applied in suspension to the inner surface of the glass discharge tube or envelope of a gas discharge lamp of the metal vapour type. The protective layer prevents contact, e.g., of mercury in the discharge chamber with amalgam-forming substances present in the glass surface of the lamp discharge tube. In addition, the crystals of the protective layer re-reflect shortwave ultraviolet radiation back to the layer of luminescent substance, thereby to generate visible light and increasing the efficiency of the lamp. The protective layer results in a marked decrease in the hitherto accepted reduction in the lamp luminance in relation to lamp burning time.