Flash tubes and modeling lamps are replacement parts for the flash light heads. Theses light are not the same as the type of light that you buy at your local hardware store. There are two types of production lighting. Continuous and Flash/Strobe which as theirs names describe create either a constant always-on light source or a quick burst of bright light. The flash tube as you might have imagined produces a quick high intensity burst of light during exposure time.
Complementary to the flash tube is the modeling lamp which is a lower output light that is constantly on.Often this modeling lamp is the"make it or break it"factor when purchasing a flash light head. They are indispensible for previewing the lighting effects to judge contrast and where shadows fall prior to making the exposure.