Use of glass in electric lamps

Abstract

The term 'glass' refers to a wide range of non-crystalline inorganic materials differing in their compositions and properties. The formation of glasses is discussed: five main types of glass, including vitreous silica, are considered and shown to meet the requirements of materials for envelopes and other components in electric lamps. Brief descriptions are given of the various stages of glass manufacture. Applications of soda-lime and lead glasses in GLS incandescent lamps and fluorescent lamps are described. Reference is made to the special requirements of envelopes for low pressure sodium lamps. Finally the properties of vitreous silica and its use in tungsten-halogen lamps, in high pressure mercury vapour lamps and in metal-halide lamps are considered and the need for the material to be of high purity is emphasized.