Hot Cathode is a type of fluorescent lamp, which has different types like hot cathode, cold cathode also electroluminescent.
Hot cathode lamp consists of a tube, closed with tungsten electrode at the ends and is filled with a gas normally argon at low pressure. Olden days, even now in some countries, they have starter start the lamp, when the power is passed through choke, which prevents short-circuit, the electrons will be passed from one electrode to the another once the ionization happens across (gas inside the tube will get ionized), an arc is formed. Starting these kind of lamp is not instant, but it glows once the arc formation remains constant.