Light exposing apparatus for forming a phosphor screen of a cathode ray tube

In combination,

• a cathode ray tube comprising
• a face panel,
• a shadow mask having a plurality of slots therein, and
• a light sensitive film secured to the inner surface of said face panel between said face panel and said shadow mask, and
• a light exposing apparatus for selectively exposing said light sensitive film comprising
• an ultraviolet light source for exposing said light sensitive film to ultraviolet light through the slots in said shadow mask,
• movable platform means producing relative movement to the light source and said light sensitive film in a plane parallel to said film,
• means for receiving and converting part of said ultraviolet rays to corresponding first electrical signals,
• signal generator means for accumulating and counting said first electrical signals to generate a second electrical signal each time the accumulated first signals reach a predetermined value, and
• means for controlling said platform means to cause a stepwise relative movement of at least one of said light source and said light sensitive film in the direction of the length of the slots in said shadow mask, said movement being determined by said second electrical signal.