Every xenon lamp from LTI has two hermetic seals that form an airtight connection for the electric current between the inside and outside of the lamp. Since tungsten is a metal and has a much different coefficient of expansion than the quartz envelope, the two materials cannot be sealed directly to each other – they would crack and not make an airtight seal.
The most reliable type of seal used in lamps to make the transition from tungsten to quartz is the graded seal. With this seal, a series of different types of glass are placed around the tungsten rod that is attached to the electrodes. These different types of glass have different expansion characteristics: glass with a similar expansion property to tungsten is placed onto the tungsten rod, and a glass with properties similar to those of quartz is placed next to the quartz envelope. Between these two types of glass, other glasses are used to form a gradual transition between them.
