Forming the bulb
2 After the glass tube is cut to length, an exhaust tube must be attached to the top. First the top of the tube is heated using gas/oxygen fires. A tungsten carbide wheel folds the softened glass over to form a dome shape containing a small hole.
3 A smaller glass tube called the exhaust tube is placed in the hole and joined to the larger tube by melting. This small diameter tube is used as a means to flush the air out of the lamp during the sealing operation and evacuate the air and introduce the fill gas during the exhaust process. This process is performed on special rotary machines.