Light bulbs and cathode ray tubes are structurally similar in some respects. For example, both contain a filament -- in the light bulb, the filament heats up to produce light, while in a cathode ray tube, the filament emits electrons, which are then steered into a target (in a CRT TV, the phosphor). Furthermore, both the tube and the bulb are often filled with an inert gas. I'm wondering if it's possible to make a cheap cathode ray tube from a light bulb. Presumably, there are some electrons emitted from the tungsten filament via thermionic emission. Can those electrons be focused into a beam by external circuitry?