 The human eye retains an image on its retina for about less than a tenth of a second. That's called persistence of vision. See, television doesn't have to show a continuous picture. It replaces each and every line that makes up the image in less than that fraction of time. That's why we need to coat these cathodes with something they can blink on and turn off. When the electrons light up, the phosphorescent dots on the receiving end, your brain can assemble all that into a steady picture because of how the vision persists. What's that?