Electrophotographic screening of color picture tubes

Almost all color picture tubes have screens composed of more than a million dots of phosphors, one third of which are green, another third blue, and the remaining third red. Each dot is accurately placed in relation to an aperture mask and one of three electron guns inside the tube. This is accomplished by optically exposing a photosensitive material containing phosphor through the shadow mask with a light source simulating the electron beam source. The exposed areas become insoluble and the screen is rinsed with water to remove the photosensitive material and phosphor from the remaining areas. This is repeated for each of the three color phosphors. Typically, exposure times are long, screens use less than one-third of the phosphor applied to them, and the phosphor is discarded or reprocessed.