INTRODUCTION A Gas filled tube is essentially a vacuum tube filled with small amount of inert gas, these gases includes Argon, Neon etc. Like any vacuum tube it has a Cathode, a Anode, a Heater (present in Hot Cathode Gas Tube) and a Grid (depending on the type of gas tube, whether it is a triode or diode). THE BASIC DIFFERENCE BETWEEN A GAS TUBE AND A VACUUM TUBE IS THAT IN A GAS TUBE DUE TO THE PRESENCE OF THE INERT GAS, WHEN THE IONIZATION STARTS IT IS RELATIVELY DIFFICULT TO CONTROL THE RATE OF IONIZATION AND DUE TO THIS IT OFFERS MORE CURRENT FLOW COMPARED TO VACUUM TUBE. EVERY TYPE OF GAS OR VACUUM TUBES GLOWS DEPENDING ON THE VOLTAGE ACROSS THE ELECTRON PATH AND THE INERT GAS IN TUBE OR COATING ON GLASS. FOR EXAMPLE WHEN THE HIGHLY ENERGIZED ELECTRONS HITS THE PHOSPHORESCENT COATING, IT WOULD CAUSE IT TO GLOW. CHEAT 1 Question: I assume you all have seen a tube light, can you identify just by seeing which end is cathode and which end is anode ?