Cathodoluminescent light source

With the right applied voltages, a cathode ray tube can certainly be used as a source of light. Here I used a small oscilloscope CRT which is internally coated with a green zinc sulfide phosphor activated with copper and aluminum. I applied about 3 kV to the accelerating anode, with the cathode and grid at ground potential, and adjusted the voltage on the focusing anode in such a way that I would get the broadest spot possible on the screen. The feed current, excluding cathode heating, is about 5 mA, which corresponds to a dissipated power of about 15 W, clearly too much for the electron gun (see picture below). Interestingly, the electron density in the tube is so high that a significant amount of charges flew directly back to the cathode, exciting some residual phosphor particles present on the surface of the electron gun and of the neck section of the tube. There's even some blueish-white glass luminescence visible on the top right corner of the picture below.