Element that emits light (red, green and blue light as used in video displays) when it is bombarded by or excited by electrons. Phosphors are placed on the backside of a cathode ray tube’s glass or plastic screen. The electron gun of the tube emits electrons, which are in turn directed by the deflection yoke. The electrons are aimed at particular phosphors. Those phosphors are excited by the electrons inducing the phosphor to glow or give off light. hree phosphors (phosphors that glow red, green and blue) are located together to form a phosphor triad. These color triads make up the pixels of a video display. When the three color phosphors are excited to various levels, their light blends together to form a wide array of colors.