A fascinating video from one of my favorite channels on Youtube, the Slow Mo Guys. We all understand the concept of building an image on a CRT screen by scanning the electron beam left to right and top to bottom, but in this video they use an ultra high speed camera to see the process as it occurs. At 380,000 fps, the individual scan lines can be seen as they are drawn left to right. They also look at LCD and OLED displays in the video so you can see how these technologies differ. The CRT part is approximately 1:44 - 4:05.
https://www.youtube.com/watch?v=3BJU2drrtCM