shadowmask

A shadow mask is a component used in older cathode ray tube (CRT) televisions and monitors to ensure that electron beams accurately strike the correct phosphors on the screen. The shadow mask is a thin sheet of metal placed very close to the phosphor-coated screen. It contains a precise pattern of tiny holes or slots. Three electron beams, one each for red, green, and blue, are fired from the electron gun at the back of the tube. These beams are directed towards the screen by deflection coils. As the beams pass through the shadow mask, the holes or slots allow only the intended beam to reach its corresponding colored phosphor dot or stripe. For example, the red beam is shaped so that it passes through a specific set of holes to excite only the red phosphors, and similarly for the green and blue beams. This precise alignment is crucial for producing a clear and correctly colored image. Any misalignment could result in color fringing or a muddy appearance. Shadow masks were a key technology in enabling color display on CRTs.