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The picture tube

The front of the tube is phosphor coated. This phosphor gives off light when hit by a high energy electron. The electrons are emitted by electron guns, located in the neck of the tube. The guns emit more electrons when they are warm. Hence the presence of the heating filament. That's the thing we can see glowing in the neck of the tube.

When leaving the gun, the electrons don't have enough energy. To increase the energy, a high voltage is applied. This high voltage, which can be 25.000V or higher, remains on the tube, even if the TV has been turned off! It may take a few days before the tube is discharged.