It is well known that the glass used in the lighting industry is not the normal window or bottle glass, but the reason why might not be so clear. This article provides an overview of the manufacture of this type of glass. There are special requirements for lamp glass which mainly focus on the part of the lamp known as the "stem." The expansion, heat conductivity, colour, light transmission & most importantly electrical resistance have to fulfil specific requirements for specific lamps. Glass used for the bulb of any incandescent lamp can be any kind of glass, the only important requirement is the price. An example of a special glass for lamp-making is so-called stem glass, where the stem is the electrical feed through the lamp & therefore needs high electrical resistance. To increase electrical resistance, large & heavy metal oxides are mixed into the glass.
