What are the different types of electrode-lamp seals?
There are two types of sealing of the electrodes to the quartz tubes, namely, tungsten rod seals and end cap seals. The tungsten rod seal is made with glasses having thermal expansion intermediate between tungsten and the quartz envelope to reduce the stress arising from thermal expansion at material interface. Since this structure (graded seal) is processed at high temperature, flash lamp operation at high current densities with long life is possible. In end cap seals, a circular band of invar, constituting the end cap is incorporated with the quartz tube. It is also called solder seal as lead-indium solder with relatively low melting point, is used to make the seal due to its low manufacturing cost. Since the solder material has a low melting point, it cannot withstand high temperature and high current density, in comparison to rod seals. This limits its operation to moderate current applications.
