Using three electrons can have problems. One is that the electron gun responsible for one colour will at one time or another light up the phosphor of another colour. Is would distort the colour displayed on screen, so manufactures have designed 3 different ways to prevent this.

INVAR Shadow Mask
This technology was designed first, and is used in televisions and most computer monitors. What it is, is basically a very thin sheet of metal which has tiny holes punched into it which are aligned and positioned to only let the correct electron beam hit the coloured phosphor it is responsible for. One downside of this technology is that it will absorb a lot of the electron's that will pass through the mask, because the holes need to be very small to do their job properly. This will make the use of a lot of electrons to create a bright image, increasing power consumption. While these electrons are being absorbed by the shadow mask, they will cause the metal in the shadow mask to heat up. The current material used is a nickel/iron mixture called INVAR that has nearly zero expansion due to heat. Older materials that expanded more due to heat would distort the image on screen. The use of a shadow mask necessitates that the screen is to be parabolic in shape in not only the horizontal direction, but also in the vertical direction so that the shadow mask can correctly filter the electrons.

Aperture Grill
This technology was originally designed by Sony, and is more expensive to manufacture then the shadow mask technology. Aperture grills are composed of thin wires drawn vertically up and down the screen. This allows for brighter images because less electrons are impeded, with a more efficient filtering. A major downside of this technology is that as the wires heat up, they will expand and begin to bur the image. To prevent a blurred image, multiple thin horizontal "damper wires" are used to tighten the wires. These "damper wires" can become visible with bright colours because they themselves can block the electron beam.

Slot Mask
This technology was recently designed by NEC and Panasonic as a hybrid of the shadow mask and aperture grill technology. It is still a shadow mask, but differs in hole arrangement. The holes are oval shape instead of round. This compliments the oval shape that the electron beam forms, more correctly filtering the beam resulting in a better picture.

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