When does light occur on a television screen?

Light on a television screen occurs when an electron beam strikes a surface covered with phosphors. In traditional cathode-ray tube (CRT) televisions, the screen is coated with luminescent materials known as phosphors. When the electron beam, which is a stream of electrons generated by the television’s electron gun, hits these phosphors, it causes them to emit light. This process is fundamental to how images are created on CRT screens, where different phosphors are used to produce the primary colors of light (red, green, and blue), resulting in a full-color image.

While electricity does indeed flow through wires in a television, this is not directly what causes the emitted light on the screen. Simply turning the screen on does not guarantee that light will be produced without the interaction of the electron beam with the phosphors. Similarly, light hitting the screen from an external source would not generate the necessary illumination associated with the display's functioning. The interaction between the electron beam and the phosphors is the critical step that produces the visible light we see as images on the screen.