Each electron transfers its kinetic energy to the picture tube screen upon impact. What is the power delivered

Answer 1

Power = E x I, where "E" is the voltage accelerating the electrons toward the screen and "I" is the electron current hitting the screen.

If the accelerating voltage is typically regulated at 20,000 volts or so, and a typical electron beam current might be 1 to 10 milliamperes (0.001 to 0.010 amperes), then the power would be in the range of 20 to 200 watts. Except for a very small amount that is converted to visible light, this power appears as heat dissipated in the phosphor face plate.

Bear in mind that the image on the picture tube screen is formed not only by scanning (a raster) but also by modulating the current of the electrons impacting the screen. In general, more current means more light until the phosphor saturates and cannot produce any more light.

A lot of the power in the electron beam of a color television is wasted because some of the electrons never reach the phosphorescent screen. Instead they are intercepted by a shadow mask or grill that is only there to make sure each of three electron guns illuminates its own color and not its two adjacent neighboring colors.